Well, my answer may not be liked, but I say bite back. My sons have only bitten me once. They went through this phase of "what are these new things in my mouth? I wonder how strong they are?" Don't get me wrong, when I did the biting, it was only to show them that their teeth can hurt others. After that, catching them in action and saying "no, not nice" was enough.
This is what worked for us.