The saying goes like this: "The only thing two dog trainers can agree on is what the third is doing wrong." While not exactly accurate, there is a shred of truth there. Dog training methods are somewhat like religion and politics in that each trainer has an opinion and we are convinced that our way is the "right way."
While there are lots of ways to approach a problem, and plenty of tools available to trainers, one thing remains the same: the science never wavers. Research in behavior science has shown that behavior that is reinforced will be repeated. Behavior that is punished is suppressed. Behavior that isn't reinforced simply goes away.
Notice that punishment only suppresses behavior – it doesn't get rid of it.Yet so many trainers are devoted to the use of punishment. Usually called a correction, trainers rely on punishment as the primary method of getting rid of behavior. And sometimes punishment looks like it works, which makes it reinforcing for the person using it. It's a tricky trap – because what you see isn't always what you get.
Sometimes the dog associates the punishment with the person – so the "bad" behavior doesn't happen when the person is around, but the minute that person is gone, the "bad" behavior comes right back. A good example of this is going to the bathroom in the house: the dog goes into another room to do his business. Why? Not because he "knows he's bad," but because he never gets in trouble for going to the bathroom inside if the person isn't in the room. The dog doesn't really understand that he should go outside – he only knows to get away from that person. That's not at all what you're trying to teach the dog, is it?
In more serious cases, punishment can lead to fear, anxiety, and even aggression.Your dog growls, you yell at him. He growled because he felt threatened or was afraid, and you yelled. Do you think you helped the situation? Sure, the growling went away, but the underlying cause didn't. Now, the next time your dog feels threatened or frightened, he'll skip the growl and head straight for the nip or the bite. Not because he's necessarily an aggressive dog, but because the person punished the growl but never got to the root of the problem (the fear or anxiety).
Finally, you can't teach a dog what TO DO by using punishment. Punishment only suppresses behavior – it doesn't help the dog figure out what TO DO. Don't waste your time using punishment – you're only suppressing behavior at best. Instead use positive reinforcement and teach your dog how to behave. Positive reinforcement will give you more of the good behavior. It's much easier to teach the one or two things you'd like your dog to do than spend your days yelling "No!" (More fun for you AND the dog.)