How do you deal with a kid that is extremely delayed and doesn't seem to understand anything who is biting themselves really hard? He is not breaking the skin but is leaving marks for hours. He is also hitting himself in the head (side of head, mouth, eye, cheeks). If I pin his arms down it seems to make it worse. Telling him no doesn't do anything. He does it 50% out of frustration and the other times form who knows what reason.... he is doing it very hard and repeatedly.