Terminate. This is not a toddler, and assuming his language skills are developed, and he is not developmentally delayed, then this is extremely inappropriate and dangerous behaviour. If you can't get full parental support to ensure consistency, then it's time to go. I'm sure your other clients must be growing angry with these incidents as well. In the licensed centre I worked in, biting, especially any broken skin, was a serious occurence, meaning that the supervisor and area manager and possibly the ministry might become involved in the case. Don't take it lightly.