aggressive dog behavior

Well, you need a muzzle to start your training, if the dog is that bad. That way if he lunges or tries to attack he can't bite. I suggest when walking him if he starts acting aggressive towards anyone, turn around immediately and walk the other way. Once he is calm turn back around and try walking him back towards what ever caused his aggression. Note this will take time and patience. Once you can get him to not lunge or growl while waking by people and dogs, then take the muzzle off and see how that works. Keep in mind that you should have it with you just in case.