Welcome to Just Answer. My name is Jane. I have been involved professionally with dogs in the healthcare and behavioral fields for over 20 years. I’ve worked as a Vet Assistant and Behaviorist and have extensive experience in dog reproduction, as a breeder, for even longer than that.. Canine behavioral issues and training are also my specialties. It will be my pleasure to work with you today.
The first thing I would do is have him tested for hypothyroidism or other medical causes for sudden aggression. Read about these here:
If there is no medical cause for the aggression, then it is strictly behavioral. Dogs are aggressive toward people for a variety of reasons. It might be that they are fearful of people and thus are aggressive before the person can be. In other cases, a dog is aggressive in order to dominate the people. Other causes could be that the dog feels they are the alpha member of the pack and as the alpha member they must protect the pack (you) from threats (people).
In addition, owners sometimes make the situation even worse by tensing up and worrying about what will happen. The dog senses the owner worry and feels that he is justified in his aggressive stance because you are obviously worried about the people. They don't know you are worried about them attacking, they just feel that you are worried and assume it is the people.
For a dog like this, total control is necessary. This means not only physical control but on a mental level, you must be the boss. To accomplish this, you will need to have the dog wear a basket muzzle anytime he is not in your own house or yard. This will not only prevent bites but also allow you to feel more at ease when walking him or having him loose.
You will need to have him obedience trained. If you can, I would do group classes (with the muzzle) and let the trainer know of the problem your dog has.. The following site is helpful in helping owners train their dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.
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.
This obedience work establishes you as the leader of the pack and as the leader it is your job to protect the dog and not the dogs job to protect you. Now the dog will still protect you if something should happen because you will be protecting yourself and as part of the pack, he will follow your lead and protect as well. But if you are calm around someone, he will see that you are ok and there is no need to help. This is why being the leader works well.
You will also want to keep a leash on him at all times initially to grab if he should disobey. I think you will be pleasantly surprised at how well your dog does with training. Dogs like knowing what is expected of them and they love the little paper thin slices of hotdogs that I use for treats while training. Give this a try and see how it works for you.
Unfortunately, at this point, I would seriously consider having a behaviorist anyway available to evaluate the dog and determine the aggression level. In the meantime, institute the techniques I have recommended.
These suggestions should help the situation a lot. I hope I've given you great service. If so, I'd appreciate a 5 star rating. The rating should be based on my answer and not any site issue. Experts are not compensated until a rating is done. If you have any other questions at all, please reply here and I'll be happy to follow up with you even after you have rated. .