Yep. A zero-tolerance regarding boarding people who have had alcohol. The rules are in place already, but they are not being enforced by most crew members.
It is very very easy, and fully legal. Deny boarding to anyone who have had alcohol or in any way behave like they had (The latter can be tested with a breathalyser if they behave drunk, but deny being so.The police is generally happy to help with these issues).
Then stop serving more than 1 or 2 units to any given pax onboard.