I recently had an interesting conversation on a training forum that I frequent. The original poster was asking how positive reinforcement trainers could possibly go throughout the training process without ever telling their dogs "no" or correcting them for incorrect behavior. She used the anecdote of her dog who almost ran off after a small animal. She told the dog "no" in a strong voice and the dog stopped in it's tracks. In her mind, this worked and there was no need for any other training. She reasoned that if R+ (positive reinforcement) trainers ignored bad behavior and only rewarded good behavior, her dog would have run away chasing the small animal.
This is a very common misconception about R+ trainers. During a training session, we will ignore behavior we aren't looking for and reward behavior we want. For example, if we ask the dog to sit and the dog instead lies down we won't punish the dog for the down we will instead either ignore it and wait for the dog to sit or lure the dog into the position we want so that we can reward him. The behavior that gets rewarded is the behavior that the dog is more likely to repeat in the future. Many people assume that this goes for all behavior. If the dog is eating your dinner on top of the kitchen table do you ignore it and wait for the dog to get down so you can reward them? Absolutely not. Ignoring a simple mistake during a training session is not the same as ignoring obviously troublesome or dangerous behavior. We will stop the animal from doing the behavior we don't want, physically if necessarily. We will not, however, punish the dog with aggression and physical abuse. Why? Because the dog is just being a dog and it was our responsibility to keep them out of trouble in the first place.
So will we say "no" to our dogs? I don't necessarily have anything against saying "no" to a dog. In an emergency situation we do what we must to keep our animals safe. In my experience though, owners rely too heavily on the word for training and end up adding more and more aggression behind it to get what they want. The more it's used the more it becomes a wasted word, which leads to frustration in the human, which leads to a louder and more aggressive no. It tends to be a downward spiral of frustration and aggression for both the human and the dog.
"No" is just a word and dogs don't inherently know what it means. What they are responding to probably has more to do with the frustration and aggression in our voice when we yell it at them for doing something we don't want them to do. Our goal as R+ trainers is to teach the dog what we want them to do so we don't have to tell them no. Management and preventing them from doing the "bad" things is a large part of R+ training. We don't wait for them to make a mistake so we can punish them. We teach them the correct behavior so they are set up to succeed every day.
So, in the original anecdote of the dog running off after a small animal. It is the owner's responsibility to prevent the situation from happening by keeping the dog on leash or in a secure area. Instead of relying on the "no" we would teach the dog a behavior we would prefer, such as a very strong recall cue. This training needs to be done before you ever need to use it in real life. As another trainer commented on the same post, "You train your dog FOR the situation, not IN the situation."