Why thank you Villette.
If he's aggressive now, it will only get worse if not addressed. Sometimes it's frustrating and sad because you have to punish them but it's better for them anyway. If I were you, I would get a leash (not the one you use to walk him with so he doesn't associate it with punishment) and tie him up to a spot when he gets aggressive, and then if he continues, spray him. He has no where to go. The longer he is aggressive, the longer he will stay tied up with no fun. He will get it eventually. I promise, it gets easier.