I catch a canine to the knuckles or backside of my hand right in the bone almost daily. It is always in an effort to teach my boy that people hands don't go in his mouth. He has learned everything else I have taught him with incredible speed and ease. I think he has some mental block about my hands and his mouth though. And only the hands... Faces he only licks, even if he is all riled up. Arms, are meh, whatever... to him. Legs, feet, torso... He could care less, but the dang hands, he just must put them in his mouth. Never a bite, just mouthing, but dang if those canines don't hit the bones enough to make me grimace a bit.
One day I WILL win this one, until then... Keeping a chew toy handy for the quick redirect!