No LisaLisa, my point is rather that this is already what your child does? She told it to stop. The dog then attacked again, didnt it?
This morning dd1 aged 11 heard ds chatting in his cot and was about to open the door to get him when she heard a big thump and heard ds shout " No doggie - you hurt [ds name] again. Bad doggie [ds name] won't play you now" . She then heard ds scream out loud " Ooooouuuuchhh -" and start crying "mummy mummy".
I dont think children that young do that kind of imaginary play! Dog bite, child scolds dog, and dog hurts the child again. Very unusual.
Which is why I dont think that teaching him to say stop and dont do it, and go away wont necessarily work.
Have you tried asking questions about the dog? Maybe you could take him to a toyshop and look at jellycat and other soft toys, and ask which most resembles "his" dog? Maybe buy him the dog? See what happens if you let him have a "real" toy dog to play with? Ask some questions, such as "is the dog hurting you?" "Is the dog nice to you?"
Children sometimes do see more than grown ups do. There used to be a storage shed for fallen soldiers during ww2 on the land we built our house on. We've had the priests around, to put it that way.....