Originally Posted by mdreckmeier
but teeth should never touch skin,
Well this is not true, but you must teach bite inhibition. Good links in the reply above. Now of course, if you do not ever want your dog to play other than with toys then of course you can go that route and train for it.
I only the other hand, like to train bite inhibition as far as teaching them how to play correctly and not hurt with their mouths. Dogs love to play with their mouths. So through a lot of training, Boa and I always play and wreslte and he uses his mouth and teeth touch skin, but thats all they do, they touch skin, they do not bite skin. This way Boa is free to play the way he likes to play and I do not get hurt. (Well, I do get hurt, but never from his mouth or teeth, always from his paws and his strength, lol, but thats another story).
I wish you luck. Keep working on the bite inhibition. Boxers are smart, he will catch on. You can definitely train him not to use his mouth for playing (or teach him to only play with toys, not flesh). The links posted above will teach you how you want to go about it.