Behavioural issues with my son

Hi, I have a nearly 8 year old, and long story short he and my daughter haven't seen their dad for 3 and a half years. His choice we have done mediation etc nothing has made him want a relationship with his kids. Anyway, my son is really suffering and has anxiety and behavioural issues as a result of this and today he threw a rock at a girl and also
Injured another boy by throwing a fence Pailing while all playing together! He makes really silly choices and he is becoming a bully! I don't know what to do anymore I am struggling to find ways to make him realise how dangerous his choices can be and I don't want him continuing down this path! Please help!