Many people don't like the idea of a shock collar on their dog and I was one of those people before too. This was before I was educated on how to use it. I hate when trainers get an aggressive dog and they put the dog in a situation that evokes aggression and then they zap him with 1000 volts. Ok maybe it's not that high, but you get the point. Its not training and usually doesn't address the dogs underlying feeling. Sure the dog will stop the aggression. If you zapped me every time I looked at a girl, best believe every time I thought a woman was coming my way I would look towards the ground. But not willingly. All you did was make me afraid to do what I still want to do.
The first step that I use is to condition the dog to the shock collar.