Anger management for son with ASD

Hi , My name is jez and i have a 9 year old son with high functioning autism. He is very bright and he is wonderful but recently he has been taken out of the classroom every day due to his disruptive behaviour. Today he was excluded for violently attacking 2 children and a teacher. 

The school have always been very helpful and supportive and we have accessed support from the childrens centre, local camhs, doctors, psychiatrists and nurses over the last 4 years, it has recently been decided that therapies are not beneficial to him as he refuses to engage. 

His father and I have tried every strategy we can think of and everything that has been suggested to us from the services. But now, we are stuck. My heart is breaking because i dont want this for him, if we cant keep him on the right track im afraid that he will suffer and his future will be bleak. 

Does anyone have any suggestions that can help us manage the violent behaviour? We have nowhere else to turn xxxx