Just lately it has occurred to me that saying "No hitting" is the same as saying "Don't hit". You will have heard that children often don't hear the "Don't" when we use that word, partly because we haven't got their attention first. You see, they are intent on doing whatever they are doing, so of course they don't hear the first word. So therefore hearing the word hitting, reinforces the idea of doing hitting, not of stopping it. That is the word they hear.
So if we apply this reasoning to "No hitting", is it not the same?
So I suggest that instead of using the word of the action we want them to stop, that we use the word of the action we want them to do. It could be "Stop". Better still, put their name in front, so that we gain their attention first. (Except that sometimes it is imperative that the child stops right then - the child will hear this in your voice tone even without their name first.
Think of the confusion a child may feel when s/he hears "...... hitting" and yet the adults are cross or seemingly wanting something else to happen........but what?? How is the child supposed to know what action the adult is wanting. Help your child focus on the behaviour you want by using the words that describe that behaviour..
The other part to consider is that to stop mid stride in an action, is difficult, and more especially when there is no instruction given about what to do. How does one change one's plan in the middle? Unless there is verbal support to know what to do.