Thanks for the additional information. It does sound like he isn't getting enough exercise and may be getting frustrated. There are some things we can do to help with what you are experiencing. One thing is to make the walk a very fast paced walk that doesn't give him time to jump up. He shouldn't be given time to sniff or investigate on the walk. You should walk to a destination where you will allow him to walk around, sniff, and eliminate for 10-15 minutes before again walking home at a fast pace.
I am also going to recommend that he wear a back pack that you can add rocks, bottles of water or cans to. this will add additional weight and help tire him out faster and keep his feet on the ground. The other thing you should do is practice obedience training daily. I have a great site that help teach obedience. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.http://www.schutzhund-training.com/training_theory.html
Training works best if you train at least 30 minutes a day (two 15 minute sessions). I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below. http://www.pets.ca/articles/article-dog_nilf.htm
Once he is listening consistently, you can use this to stop his jumping up and nipping by commanding him to sit or lay down. I recommend a high value treat like a hot dog slice or liver sliver. Until your dog is obedience trained, there is a method I've used for over 15 years and is very effective and not cruel for a dog that jumps on people. It cures even the most stubborn large dog. However, everyone in the family will have to be consistent until he learns it is not acceptable.
What you will be doing is putting one knee up to waist level any time you see the dog start to jump up. Put it up before the dog is close to you, so he sees it. YOU DO NOT KNEE THE DOG. Instead you put your knee up long before he reaches you and he jumps onto your knee generally hitting himself in the chest as a result. Since your knee is up and you aren't moving when it happens, he does not interpret it as something you are doing. At the same time you need to say in a low toned firm voice, NO JUMP. He'll learn that when he jumps, he ends up hitting his chest and will associate NO JUMP with that feeling and learn to not jump on people. He may still dance around on his hind legs, but they do usually learn not to touch the person. Again, I want to stress that the knee should not be used to hit the dog, but instead let the dog run into the knee.
Your dog may try and come at you from the side, but just shift position until he learns that he can't jump. You can stop nipping from behind by adopting an exaggerated walk bringing your heels up high in the back. When the dog tries to jump up to nip, they get a heel in the chest. They don't think of it as you kicking because your back is turned and you are just walking. They learn pretty quickly to not do that.
The instance where he is getting frustrated because he can not get to another dog is often referred to as misdirected aggression. I think you handled that pretty good. The obedience training, pack along with the "NO" and quick tug should help with this situation. If you carry some of those high value treats, and get your dog's attention before he fixates on another dog, you may be able to keep his attention on you and help prevent it as well. Just remember to only give a treat when he is acting the way you want and do not give it to stop the behavior. Reward desired behavior.
Remember that the behavior did not start overnight and will take time to stop as well but these techniques and tips should help. Also you should not force a dog to submit to you physically. It just teaches a dog that physical reprimands are acceptable. A reprimand might be a nip to let you know the dog finds your behavior unacceptable. Now if you command your dog to lay down and stand over them and they submit, that does show the dog is submissive to you. An obedience trained dog usually just obeys.
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