Maybe the proposed solutions and approaches need to be more creative. I'm distressed that his therapist bailed out because he tested positive for marijuana, although I do know that some therapists make contracts with people to treat them as long as they stay off drugs/alcohol. I find that approach very counter-productive and punitive.
I would have no problem professionally with your searching out some private schools and military schools that are experienced in dealing with kids who are behaving like your son. I would be very careful to select one(s) that rely on small classes and individualized comprehensive treatment rather than punitive measures. I'd also search for a therapist who would hang in with your son, challenge him and support him. Your son should be allowed to participate in these choices, but don't be surprised if he plays the role of resentful, angry victim. Some professional counseling for you, especially during these tough times, would be a good idea.