Easy solution to that:
Breathalyse them before they get on the aircraft.
This has already started in India:
Breath test for all pilots
TNN, Jan 15, 2011, 06.35am IST
CHENNAI: Reporting for duty after consuming alcohol is going to be extremely risky for pilots hereafter, as airlines have started doing pre-flight breath tests on pilots of all departing flights as part of Directorate-General of Civil Aviation (DGCA) instructions to make such tests compulsory.
Earlier, such tests were conducted randomly. Now, with the procedure being made mandatory, airlines have to make an additional investment on the automatic Alco Sensor machines, as per DGCA specification.
Sources said Air India and Jet Airways have started testing all their pilots from the first week of January. As the tubes used to test pilots and cabin crew are disposable, airlines have started bulk-ordering the tubes...
Breath test for all pilots - The Times of India