Unfortunately, this is your dog‟s temperament. But the good news you can control it, not eradicate the aggression. Sometimes shy dogs act aggressive to ward away the object that is frightening them but don‟t really want to harm the object, other times there is a bite. Aggressive dogs, on the other hand, hold a certain „prejudice‟ towards strangers (animal or human). In my opinion, no dog that is shy can be taught to be outgoing, nor can an aggressive dog be taught to be friendly. BUT, a dog can be taught to ignore the fear or the object (human or animal) that it wants to be aggressive towards. Through obedience (and major repetition) you should be able to teach your dog to focus on you, its “Alpha” (or leader), rather than “the Object” (human or animal). This way your dog will understand he is being corrected for not paying attention to your commands rather than being corrected for being afraid or having a distrust of people. In the world of dogs, the “Alpha” is the decision maker. The “Alpha” protects the pack and its territory. Another dog in the pack that does so is challenging the “Alpha” for that leadership position. Don‟t allow your dog to think he is “Alpha” and that it is his job. Give your dog a command and he will believe you are taking control of the situation and he doesn‟t have to. If your dog has confidence in your ability as “Alpha” he will always obey your commands because doing so shows respect to the “Alpha”. Aggressive dogs believe they are “Alpha” until you prove them wrong, and shy dogs don‟t want to be “Alpha” it actually causes them too much stress. Once your dog has confidence in your ability to be “Alpha” then he will trust your judgment under any situation and allow strangers in your home.
My recommendation would be private training and then possibly group classes. NEVER ALLOW YOUR DOG TO MEET ANYTHING HE IS AGGRESSIVE TOWARDS. He doesn’t have to like anyone he only has to ignore them and obey your commands. Tell your guests to ignore him, always keep him on a leash and under a command and NEVER TRUST HIM. YOU NEVER KNOW WHAT ANY DOG IS GOING TO DO. He may be part of your family but he is a dog. Treat him like a dog and he‟ll know what is expected from him.Without strict leadership the training will not work.
Remember that this is not basic obedience; you are making him control his aggression not become „Lassie‟. Your dog has the potential to hurt someone. HE BELIEVES HE IS THE LEADER OF HIS PACK and that he is doing his job. You are going to have to be tough and make him realize it is not his job to protect you and that you are not flattered by this behavior.