I tend to use no as a safe word, in the theory that no means no. This in spite of knowing that no does not always mean no. Some people like to say no when they are in play, and this can cause confusion.

In most cases a simple talking about the meaning of the word no, and my intent to stop when I hear it, is more than enough to cure this. There is an occasionaly exception, and this makes it necessary to have a safeword in that instance.

That said, that is my personal preference, and I advocate for safe words at all times. It is just that I choose to use no as my safeword most of the time to avoid confusion. I have found that during an intense scene that a safeword can sometimes be forgotten, and that a sub will panic and make it worse. This is why I prefer to train a sub to not say no unless she means no. If a sub does have a safe word it might make her feel more secure, but I would still prefer to have no or stop mean exactly that.