Boundary question

I am still a little foggy on the boundary concept – well I understand it, but I keep thinking I’ll use it to teach the other person a lesson.
My husband occasionally will drive home when he’s had a few drinks and is likely over the legal limit. I absolutely hate this – I feel it makes him a bad person and I spiral into thoughts of him being caught by the police or hitting someone with his car.
I tell him that’s not on for me and he says he won’t do it again.. then a few months later he does.
Any boundaries I think of don’t really make me feel better – e.g. ‘If you drink drive, I will sleep in the spare room’. And as I first said, I feel my boundaries are more threats that I hope will make him stop doing it. Am I thinking of boundaries in the wrong way? Do I just accept he’s an adult and can do what he wants?