Blood test...If we can do it for thousands of drunks all over the country, we can do it for these entrants.
And even better....let it be done before they leave and let them wait the stinkin' two days for the "clean" results and attach it to their passport.
Then, for all the cheaters, take a blood sample when entering the USA.
Cheap, efficient & conclusive.
I read that Tulane University has developed a blood test that works in about 15 minutes and it only takes a finger prick for blood. The article said that the feds won't let them use it.