E.M.
My now 5 year old liked to bite whan he first got teeth. If he was mad or excited. He has always been advanced mentally, but age appropriate emotionally. I tried nicely saying no, re-directing his focus, time-outs. Nothing helped, he mostly laughed. One day I bit him back. Not as hard as I could, but hard enough so he didn't like it. He never bit me or anyone else again. It wasn't so funny happening to him! We moved on and no thought or mention of it ever came again.