First thing can I say how cute Rebel isIt sounds like he might not have learned to inhibit his biting when playing. As puppies they learn to control their biting by either correction from litter mates, another dog or the owner. Use a stern voice when he bites to hard or loud yelp, you can also spray with a water bottle or a can with coins and shake when he gets to aggressive in play. It should startle him and break his bite/ play long enough for you to correct him. Another thing you can do is put him in time out/ crate when he gets to mouthy or rough. Its tough but eventually they do get it. It takes patience
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