You would think they would know by now, with athletes in alot of different sports getting caught and it is hard to get caught.
It's hard to get caught, and my believe is because there is so much money involved, the WADA is paid by the IOC, IAAF and all the other organizations to let slip on most people. Every once in a while someone has to go because the anti-doping show has to go on, but all in all sports would be ruined if legends like Armstrong, Bolt and other would be caught.
Another thing is that the only countries with very strict testing seem to be the central european nations, on the other hand China, Russia, Jamaica are famous for drug testing much less or with warnings in advance.
No wonder US athletes have their "training camps" in 3rd world countries or in Jamaica, even Japanese athletes go to these camps in China, all methods to avoid off season testing.