My boy Tungsten is a ham and a lap dog, pretty much. When I groom him, and don't have him cross tied, he likes to "groom" me back. He is normally very gentle and only uses his lips. However, he sometimes tries to begin to use his teeth and I softly push his head away and he goes back to lips.
I don't want to totally discourage this behavior because I see it as good bonding time. Any other suggestions as to how I can discourage rougher "grooming" without being to harsh.