Please don't bite your puppy. You are not a dog. Your puppy is smart enough to know that. Use GENTLE or EASY to remind him that you want to keep your hands and fingers.
Scruffing him is ok to let him know he can't do that. But I would remove my hands from wherever he was trying to eat them. And if he went for my legs, I would scoop him up and dump him unceramoniously in his play area for a time and would ignore him for a bit. He needs to know that when he gets too rough, the game is over.
As for the GENTLE command, I use food, and start with it in my open hand and say GENTLE. Generally they will take it gently out of an open hand. Always remind him for now though. Make it harder, and put it in a cupped hand, make sure that he doesn't get it unless he is taking it gently. Good Gentle, Good boy.
Now is where you lose your fingers and put it in between your thumb and fore finger -- GENTLE. Good Gentle. When he is good at that, you can start using the gentle word with other stuff. Gentle with the baby. Gentle with my fingers.
It works for mine.
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC