Very easy solution!
Simply make it a condition of employment that from 12 hours prior to start of duty on first day of flying thru finishing the last days flying NO ALCHOHOL will be tolerated.
Nice easy ground rules that anyone can follow, anyone not conforming to be fired without hesitation.
There would be no doubt and passengers and crew would be protected and much safer from those who "think" they can drink and/or take drugs with impunity and still operate aircraft.
Very harsh you might say but realistic!!