When it comes to issues of aggression, I think it'd be really best for you and him to seek the help of a Dog Behaviorist. They would be much better able to assess your situation and the environment and give you real tools to work with your dog.
There simply isn't enough information to go on here, and it'd be much safer to go by a professional's sound advice.
There simply isn't enough information to go on here, and it'd be much safer to go by a professional's sound advice.