From Bottle to Stick
Flight crew should be happy to submit to random tests for alcohol. This could be done discretely at sign-on or by a visitor to the cockpit. Company policy should be that when a crew is tested positive by preliminary test they must cease duties for the day and submit to a blood test within a prescribed time. Of course this leads to the fundamental issue of trust between the company and its employees. For this reason the basis for the test should be founded upon the insistance by the public that they be done. The best way to do this is to lobby government to enact legislation requiring the tests to be done before each flight.
As for the pre-departure alcohol-on-the-breath situation, the 180 passengers behind you will be expecting you to make an assertive decision in the interests of safety.