Safety of children / drinking & driving

I'm beyond frustrated tonight.  For many years I've tried to quietly get the keys when leaving a restaurant when my husband has been drinking.  I've tried to hide it from my child.  My spouse often argues & minimizes what he's had to drink.  We had a big blowout on the same topic 4 yrs ago.  I've been very clear that I don't want him drinking while driving or driving us home after several mixed drinks or beers -  especially not with our son in the vehicle. It's silly when I'm sober to take the risk.  Tonight while he was in the bathroom I told my son to come ride with me so he could get to bed & dad had another vehicle to take home. My son also has ADHD & began to argue that dad already said he could ride with him.  I tried making a cover excuse by saying he has to stop on the way home.  My son continued to argue & I finally said it'd be better to ride with me since I drank water & dad had a few alcoholic drinks (martinis). The arguing went on.  I told him to follow me out.  He proceeded to hide & wait for his dad to try teaming up against me.  He told my spouse my concern which elicited looks that could kill.  He proceeded to tell him to go get in his car, came & chewed me out for "throwing him under the bus" in front of our pre-teen son & told me to quit acting all "high & mighty."  I am SO tired of not being backed up, his risk taking/arguing behavior that I am beside myself.  I'm scared to move fwd with this man if he can't take responsibility & take my concerns seriously.  We have done the couple's seminar, but he's only gotten through 2 sessions.  I'm desperate for some kind of break through. Any advice?  I'm sure my son will have a lot of questions.