I have a twelve week old puppy who is Always biting! When My mom was with Finny ( thats my dogs name) one night, me and her were sitting outside one night, letting Finny run around a little, stuff like that, then he came overb and started playing with us, got to rowdy, and bit my Mom, and she almost needed a stich. Of course, Puppy's bite a lot! Right now when Finn bites, I give him a little pop on the nose, not hard at all, but just a little pop. It distracts him, and he doesn't like it, so he'll stop. When he get's a bit older, I'll start a more serious punishment like your doing right now, grabbing his mouth. Also, we have a deck and we were eating outside one night, and Finny was just alking around the deck play ing when he came under the table and starteed biting out feet. So I put Tabasco sauce on my feet. It works, and it'ssafe, my vet recommended it ! He didn't bite for at least two days strieght. One more thing, You can get something called Bitter apple spray, and when he bites, spray right in his mouth. My puppy is now scared of the bottle, and when he sees that Im taking it out, he stops biting right away. And it Can't hurt him! One last thing, if he get's to wild, put him in his crate (if you have one). It teaches him he can't play like that.