Interventions don't have to be, but really need to be done professionally. Contact a local addiction treatment facility. They will help you put one together.
You indicate that this last detox was perhaps one of several attempts. What were the circumstances that led up to his decision to seek help in the past? Lost jobs, arrest? Just curious.
Sobriety entails a whole lot more than just going through detox (you don't go into detail about this in your post). One has to work a complete program of recovery (inpatient, outpatient, AA). And even then, the outcome is uncertain at best. If he hasn't received the message of sobriety, then nothing will work for him, until he is ready to work at it.