Sorry it took me a while to answer. Holiday weekend plus computer not behaving well at all! Internet is being very slow for some reason.
Oftentimes when a puppy gets overly tired, this type of behavior occurs. Where does he sleep? It might be a good idea to put him away so he can sleep if he is acting up due to being overly tired. It always helps to have a puppy who is used to sleeping in a crate so that he has a safe, secure and private place to rest when tired.
I would not recommend holding his mouth shut or bopping him on the nose (besides you have already discovered that these do not work) - plus, they may either make it worse or make your puppy "hand-shy".
I would suggest leaving a line (you can use an inexpensive leash or cord) on him in the evening - make sure that you are supervising because it is dangerous to have a line dragging from an unsupervised puppy's collar. The line will allow you to have more control without reaching, grabbing for, or chasing your puppy.
Have you tried having a toy in your hand so that he interacts with the toy and not your arms, legs and hands?
What type of diet is he being fed? If you have him on an brand that contains corn as the first, second or third ingredient or that has any sugar, dyes, or chemical preservatives in it, it may help to switch to a better quality of food. To learn how to read dog food ingredient labels go to my web site at http://www.personalizeddogtraining.com/ and click on the "feeding" button.
Does leaving not work because he continues to run around and act crazy while you are gone or does leaving not work because he starts in again after you return? If done correctly, time-outs usually will help to improve the situation. If he continues to run around and act crazy while you are gone, instead of leaving him in an area that he is able to continue being roused up, calmly place him in a puppy pen or crate for the time-out. If he is okay while you are gone, but starts in again after you return, you need to leave as soon as he starts again - you will be doing more leaving than staying at first. The only way a puppy can learn through a time-out is with a lot of repetition. When you leave, stay gone for one or two minutes and then return. When he mouths, says "oops too rough" and leave again for one or two minutes and then return. Keep doing this until you see him trying to play nicer. However, if your puppy is acting up due to being overly tired, then the time-out routine will probably not work. If he is overly tired, then the solution is to put him away to get some rest.
It will also help to teach your puppy some self-control exercises such as "wait for treats held in your hand" and "wait for treats dropped on the floor". Puppies should always be taught with positive reinforcement - not corrections. I suggest finding a trainer that will come to your home and give lessons to your family and your puppy - to find such a trainer, visit my web site at http://www.personalizeddogtraining.com/ and click on the "puppy manners" button. In the index, click on find a trainer. The APDT and IACP web sites have trainer searches by your zip code. Also, by clicking on the "puppy manners" button you will find additional information about dealing with excitable puppies.
Following is a handout that I wrote on mouthing that will hopefully include some helpful advice for you.
HELP MY PUPPY IS MOUTHING ME!!
IN MOST CASES, MOUTHING IS NORMAL PUPPY BEHAVIOR. Some individual puppies are mouthier than others. Also, some breeds are mouthier than other breeds (for example, retriever breeds often tend to be mouthy as puppies). If you feel that your puppy is mouthing abnormally viciously, please consult your veterinarian and/or a behaviorist or a professional trainer who has experience with aggression and a good understanding of aggression. Most young puppies just mouth because that's what puppies do - on rare occasions a young puppy may actually have a temperament problem or a health problem leading to non-puppy-like vicious behavior. A puppy such as this usually will not let you touch them and/or will guard food or objects from you. I have seen a puppy such as this on a video tape and it looks much different than even a very rough puppy mouthing in play. Thankfully, aggression such as this in a young puppy is RARE. Remember, with normal puppy mouthing, it generally stops in due time. Use the below instructions to help.
MOST COMMON REASONS PUPPIES MOUTH
1. The puppy does not know better. Teach your puppy to inhibit his bite. Leave a line on your puppy's collar when supervising. If he has the habit of running past you and grabbing you on the way by, the line can be used to calmly stop him without chasing him (if you chase him, he will take this as a game and get more excited). If once you stop his rapid approach, he wants to gnaw on your hands, arms, and legs, hold his collar so he can only gnaw on one of your hands. Let him gnaw on one hand without yanking your hand away. People often flail their hands and overreact around mouthy puppies. Rapidly pulling your hand away and overreacting will excite the puppy and make the mouthing worse. Do your best to stay calm and hold your hand still as your puppy mouths it. You are initially letting your puppy mouth your hand so you can teach him the difference between gentle mouthing and mouthing too hard. When the mouthing causes you pain, emphatically screech "OUCH!", as you do this gently move your hand further inside your puppy's mouth and then slowly out again as you calmly tell him "gentle" or "easy". Praise your puppy when his mouthing is gentler. You could play the "kisses" game to encourage him to lick instead of mouth. At first say "OUCH!" only when his mouthing causes pain. Once he knows to mouth more gently, start saying "OUCH!" when you feel any pressure at all. Finally, say "OUCH!" anytime he mouths your skin. If after you say "OUCH!" he starts mouthing again, repeat "OUCH!" and leave him alone for 60 seconds - a crate may help if it is not safe to leave him alone or if he occupies himself by having fun when left alone. After the 60 second "time out", the learning will not take place unless you return to the room and try again. The "time out" teaches the puppy that if he is too rough, you won't play and coming back and trying again gives your puppy the repetition of this consequence needed for learning. You may have to say "OUCH" and leave the room several times before he gets the point.
2. The puppy is teething. Provide your puppy with toys that he can chew on to help his teeth feel better. If he chews on your hand, replace your hand with a toy. Have enough toys available so a toy is always in your reach when you are where your puppy has access to you. Toys that often work for a teething puppy are rope toys (sometimes it helps to soak the rope toy in water and stick it in a plastic bag and freeze it), marrow bones, Nylabones, and Kong toys. Marrow bones and Kongs can be stuffed with peanut butter or spray cheese to keep the puppy interested.
3. The puppy is exploring with his mouth. Teach your puppy to keep his mouth away from your hand. I teach this with a treat and the word "wait", meaning do not touch my hand to get the treat until I say OK. You may also try treating your hands and arms with lemon juice or bitter apple to discourage the puppy from gnawing on your hands and arms.
4. The puppy is hungry or underfed. Your puppy may mouth more if he is hungry. Consult your puppy's breeder, your veterinarian, or dog trainer if you have any questions about how often, how much, or for a recommendation of what type of food to feed your puppy. Caution: while underfeeding your puppy is not good, neither is an overweight puppy.
5. The puppy is over-stimulated. Work on being calmer around your puppy. This is especially important in households with young children who have trouble staying calm. Give the puppy some time to himself to quietly rest. If he is over-stimulated, calmly give him a 5-10 minute "time out" in his crate or resting area (do not act as if he is in trouble when you give him a "time out"). Teach your puppy to accept smooth, calm stroking and massage. Talk quietly and calmly and pet him under his chin, at the base of his ears, and on his chest and tummy. Do not pat him on the top of his head. When your puppy has settled, instead of ignoring him, calmly praise him (if you train with a clicker, click when he has settled and toss him a treat). He may get up when you praise or click him for settling, but the praise or click will ensure that he chooses to settle more in the future. Do not flail your hands in front of the puppy's face and do not place yourself on the floor at the puppy's mouthing level. If you or any of your family members are on the floor with the puppy and he is becoming over-stimulated and lunging at you and grabbing you, stand up, fold your arms, look at the ceiling, and gain control. If necessary, leave the room for 60 seconds before coming back and trying again (when you return, be much calmer and don't get down on the floor with the puppy). If he is still over-stimulated, calmly give him a 5-10 minute "time out" in his crate or resting area.
6. The puppy is under-exercised. I can't stress enough that a tired puppy is a good puppy. Retrieve is a wonderful game that can wear a puppy out. If he won't bring the retrieve item back to you, either sit in the place he naturally wants to bring it, play with two retrieve items and trade back and forth, or play with a rope dragging from your puppy's buckle collar. Hide and seek is another fun puppy game. Have someone hold your puppy while you hide and call his name to help him find you. Only hide in fair places: on the ground and not behind closed doors. At first hide in really easy places and let your puppy actually see you hide. Another fun game is scavenger hunt. Have someone hold your puppy and allow him to watch while you scatter small treats in the grass in an area about the size of a hula hoop. Say OK and release the puppy to hunt for the treats. Gradually increase the distance the puppy has to run to get to where you have scattered the treats.
7. The puppy was taught to play rough games. Do not play chase games or wrestling games with your puppy. Also, do not allow these games to intentionally or accidentally happen with your kids. When the kids are playing these games among themselves give the puppy crate-time, take him on a walk, or find something else for him to do. Tug games can help teach your puppy not to mouth if you play by strict rules - don't let your puppy start the game (store the tug toy out of your puppy's reach, invite your puppy to play, and put the tug toy away when you are finished playing). If the puppy mouths you or accidentally touches you with a tooth, give him a time-out. Young kids should not play tug games.
8. The puppy is bored. Bored puppies need more exercise, need obedience classes, need to practice obedience exercises, need to learn tricks, need to play games (see games mentioned in #6, not rough games), need everyday jobs, need more variety in their lives (socialization, walks, hikes, visiting different places), and would benefit from dog sports such as agility.
9. The puppy is tired. Does your puppy get a chance to get enough rest? Is someone always disturbing your puppy's rest? Make sure your puppy is on a schedule that allows him to rest peacefully. Make sure he has a place that he can call his own for rest. Crate-training is highly recommended so your puppy has a cozy place to rest that is off-limits to kids and other humans that like to disturb a puppy's resting time. Enjoy the time that your puppy is asleep!
10. The puppy is unrewarded for good behavior and seeks (and receives) attention for bad behavior. This is similar to the problem of an over-stimulated puppy - see #5. If your puppy has settled, remember to reward him. If your puppy is causing trouble, calmly attach a line to his buckle collar so you can have calm control instead of over-reacting. Puppies that seek attention through bad behavior also tend to not be getting enough exercise - see #6 - and are suffering from boredom - see #8. Crate-training will help you not overreact to a trouble-making puppy. If you need a break so you do not overreact, calmly place your puppy in his crate for a rest.
11. The puppy is irritable (this could be due to being tired, hungry, teething, in need of exercise, or due to a health problem). You need to figure out just why your puppy is irritable. Make sure he is not tired or hungry. Give him something to teeth on. Make sure he is not ill by taking him to the veterinarian. Make sure he is getting enough exercise. Follow the pertinent advice in #'s 1-10 above.
EXERCISES THAT YOU CAN TEACH YOUR PUPPY THAT HELP HIM DO SOMETHING OTHER THAN MOUTH YOU: Teach kisses - rub some meat juice or margarine on your palm and say kisses as your puppy licks it off. Practice this until your puppy licks your hand on command without the meat juice or margarine (as you practice, use less and less meat juice or margarine on your hand). ---- Teach your puppy to wait to take a treat from your hand until given the OK. Also teach your puppy to take small treats from your fingers gently. Contact a trainer to learn how to teach this.
Good luck with your puppy!