I agree that there is a big gap between how we see the course as measurers, and how it is set up-- the latter is often in a big hurry, at "Oh dark thirty", and with not enough personnel available to monitor the setup or the race itself. What to do?
One measure would be to insist that all course monitors and other personnel be given a copy of the official certification map. I think runners should get it as well or at least have it readily available. Out of all those runners and course workers, I'd hope at least a few of them would bother to compare the official map with how the course is set up.
Beyond that I agree with the kind of measures Kevin is talking about. Not sure we can get 2 measurers in all cases but for big races pre-race validation is a good idea. Also, race-time monitoring is very useful and but too rarely done. On several major races in DC where I provide this service, I nearly always catch and correct mistakes--some of those are merely inconvenient for the runner (mile marker is in the wrong spot) but many would be dealbreakers if uncorrected, like turnarounds marked a block too early, or sending runners a half mile out of the way, etc.