We had similar problems (though not as bad) with our boy. So far timeout in a kennel has been the most effective punishment. He's still nippy for attention sometimes, but as long as we head it off early he doesn't get bitey. If that fails, you could always try this, it's the only Marshall's product I ever recommend. We used it to prevent cord chewing, but it should work on skin too. Just be sure you wash VERY thoroughly after using it. I cannot stress enough how absolutely disgusting it tastes. It's not bitter apple bitter, it's bile from the last clenching puke of a terrible hangover bitter.