The most important part of saying 'No' is knowing exactly when to say it.

The problem of timing isn't limited just to this command either, it's one of the most important parts of any successful training. Training is mostly about giving feedback to the dog, feedback that is sometimes positive and sometimes negative, but every time feedback is given, the dog learns something about the situation, whether we intended it or not. As human beings we have a marvellous understanding of language, and in fact for us language has become more than a way to communicate, it has become a tool in itself and we rely on it constantly with nearly every waking thought. So it's no wonder we try to use it so much when we train dogs, it's our most natural way to convey meaning.

As far as a dog understands it, any feedback we give them is a consequence of what they just did. Good feedback is a reinforcement, something the dog likes and that makes the dog want to do the same thing again. Bad feedback is a punishment, and almost every dog wants to avoid punishment whenever possible.

What makes our feedback effective is the combination of the kind of feedback we give (reinforcement or punishment), the timing with which we give it and the level of feedback we give. A dog that understands even the first principles of training is constantly looking for feedback on its actions so it can work out how to behave to its best advantage. Most of us wouldn't have much trouble knowing what kind of feedback to give, for example we wouldn't normally yell at a dog for politely sitting near its dinner bowl when we fill its food bowl, and nor would we gently praise a dog that is about to attack us. Would would also have little trouble knowing that a dog that is not biting the person teasing it deserves much more praise than the one who also doesn't bite the person offering it a food treat. We have a reasonable concept of the type and level of feedback needed in these cases.

Most of the problems with training arise with knowing when to give feedback, and some cases are less obvious than others. Good dog trainers give feedback very well and the dogs learn to look for it.

Feedback works best when it's given exactly at the point where the desired behaviour occurs. Not while it is starting, or a moment after it has presented itself, but exactly at the point it occurs. Why? Because we sometimes forget that dogs are not in any way good at reasoning things out, something humans can do specacularly well, and feedback is lost and useless if the dog doesn't associate it with the right thing. It's too much to ask a dog that's digging a hole to understand that after it comes to you and you tell it firmly 'No!', that you were really referring to the hole digging, and not the quiet sitting at your feet.

It's also not good to give feedback too early, because the dog will be learning that performing half the command is enough. Half a sit. Half a stay. Only half good.

As for saying 'No', dogs generally come to understand that 'No' means that they should stop some specific activity, primarily because a punishment is just around the corner if they continue. 'No' becomes a warning indicator. It's a born instinct in all dogs to read and react to warning signals such as growling, and for a dog that lives with humans, a sharp 'No' often works as well as the growl of an unfriendly dog. But what is it they should be stopping?

In just one day I myself used the command 'No' to mean "Don't dig in the water bowl", "Don't chase that dog", "Don't go too close to the fence", "Don't dig in the yard", "Don't come near me I'm wearing black" and a host of other meanings, including the most bizarre one of all "Don't ignore my commands."

Only one of those 'No's was correct and it was in fact the case where my dog was digging in the water bowl. In all the other cases there were much better training approaches I could have used. In the case of the water bowl the command 'No' worked because said sharply and as a warning it actually meant "Freeze!" and was unlikely to be misunderstood. The behaviour of digging in the water was very specific, and occurring exactly at the point the feedback was given. My 'No' was an effective warning of a possible punishment to come and was taken as such. Of course it's fair to say that my dog learned nothing except that he had avoided a possible punishment, and the chance of him digging in the water bowl in the future were not changed one bit.

In all the other cases where I had used the 'No' command, the meaning was wrong and given 'No' meant 'Freeze', that really wasn't what I wanted my dog to do anwyay. Saying 'No' gave my dog no clue whether it was the running or chasing after the other dog that should stop, whether it was 3 feet or 6 feet he should stay away from the fence, whether it was the hole digging or the catching of the cricket he was trying to dig out that should stop, and that I was an unfriendly human only when wearing black.

To stop my dog chasing other dogs I could use an away 'Sit' command to halt him and displace the chasing behaviour. To stop him approaching a fence a recall 'Come' would have been the best choice followed up by formal boundary training along the fence line later, under more controlled conditions. To stop him digging in the yard I could have started a game of 'Fetch' with a stick or a tennis ball, and later put pea gravel or wire mesh around the area being dug to set up a minor aversive to digging there. To stop him approaching while I was dressed in black I could have said "Go Home" to send him away to another part of the house.

The last 'No' command I gave deserves special attention. From the dogs point of view, how ironic for me to issue a command to 'Come' and then a few seconds later (when I saw he wasn't responding to it) to follow it up with a command effectively to 'Freeze'. My dog would either learn to ignore one command or both, or learn the new command 'Come No' where he would wait for the follow-up 'No' cue to be issued before coming. Neither of these outcomes would have been good. Much better would have been to issue a release command such as "Off You Go" then walk up to him and clip on a lead, or give another compatible command such as "Home" or "Fetch" to both get his attention and get him moving. In either case the 'Come' command was not properly conditioned yet and needed more work later.

To some dogs the word 'No' is actually a comforter as well. Chronic barkers find reward in hearing their owners yell 'No' out the back door, even if it's said angrily, and ironically this often escalates the barking behaviour. If the command doesn't have the desired effect on behaviour then it's us, not the dog, that doesn't understand the true meaning of the word.