The only two ways to motivate people to follow rules are financial incentives/penalties or fear of consequences.
The only legal way to remedy the CESSPOOL of drug abuse that the UFC has become is for the athletic commissions to invoke a zero tolerance policy.
Any test whether before or after a fight, months out from a fight, WHENEVER, that turns in a positive result for ANY banned substance should be met with an automatic lifetime ban from the sport.
Literally, ZERO tolerance.
See how many "oh everyone does it" responses you get then.
Make breaking the rules a legit risk to someone's career and livelihood and see how that changes things.