Start with your working relationship. It will help if you take this dog to a group session with other dogs, so that he learns his basic obedience and learns to work together with you in an environment with other dogs and loads of stimulus. You may find, just there, you'll make great achievements with him.
Merlinshope gives fab advice here - I REALLY like this advice about group obedience training because it also gets experts (choose a RECOMMENDED trainer) looking at the situation and they often see aggression patterns first hand. You also get to ask for advice and have the benefit of the trainer's connections. It will be VERY interesting to see how the dog reacts with other strange dogs.