That is why you set the barriers very high. Allow no drinking without personal supervision. Marijuana usage punished like it is Heroin. Pre-16 YO dating not allowed. 16-18 YO under strict supervision of dating. Early curfews, check out their friends parents, disallow sleepovers you cannot be sure of...etc. Kids are going to break the rules, let them do it by smoking a little pot or drinking some beer. If you allow pot and drinking, they will step over a different line...Cocaine, meth, heroin etc.
"When you work like a man you can drink like a man" was one of his sayings.
My mom hated it and thought I was being corrupted. But those were some of my most pleasant memories with my dad - who was otherwise very strict and not much for words. He did say more than one time that if he ever caught me messing around with drugs, he'd throw me out of the house and disown me. I think he was dead serious too.
Those early beers satisfied my curiosity about alcohol and I never had anything to do with drugs. And my school was a hotbed for drugs of all kind. I stayed away from them and the kids that used them.