Growls...for toys only seems to work
Our 4 month old female Boxer puppy has been taught that growling is reserved for toys only, but shouldn't be included in play with humans. So far it seems to be working. If she gets too rambunctious when she is playing with us and we hear a soft, muffled growl, we all say "NO!" at once and she becomes mute and continues to play with us. We DO allow barks of joy...when we get really going, playing with balls, pull toys, stuffed toys, etc. But no growls or biting when playing with humans of any size or shape.
She has a large lifesize plush stuffed dog we purchased for $10.00 at local KMart store (she has had this toy since she was 7 1/2 weeks old and it is still in one piece!) and she is allowed to growl at this fake dog all she likes...and SHE DOES. We were afraid maybe it would teach her to grab other real dogs, jump all over them, bite their backs and necks and growl while jumping in a circle with her forearms wrapped tightly around them...but no, she never even barks or growls at any real dogs she sees or meets close up. She stays mute and just wags her stubby tail. Apparently she knows a fake dog from a real one!