You need to learn how to give a motivational correction.
You should first properly size and fit a pinch collar and tab (a 3/4′ leash) on the dog, and anytime he bites, give him a “pop/tug” and “release” on the leash (tab). I can guarantee you that your dog will not continue to do a behavior which does not feel good.
This technique always works… just use common sense, read your dog, and be careful not to over-correct. But at the same time, make sure that the correction IS motivational. I.E., if the dog keeps doing the behavior, that’s usually a good sign that your correction isn’t motivational.
After you correct him, then offer your hand again, to see if he’s learned. If not, repeat the procedure with a more motivational correction. Make sure that you’re “tugging and releasing” the leash, rather than “pulling.”
The difference is that when you “pull” you’re not using slack in the leash. If, when you offer your hand, he refuses to bite it, then praise him as he’s made the right decision.