I had a biter. It's 'orrid. What worked for us was that every morning we'd draw a train on the whiteboard. If he bit anyone, the carers would rub it off and that meant no playing with trains that evening at home.

How is his speech? A lot of it with Pip was his inability to communicate, and his frustration. Using some cards like "stop" does help. I know how you feel, I spent so many hours crying about his biting. Biting back achieves nothing.