Most doping is actually not supportable on an individual basis. It is program based. It requires the collusion of coaches, training partners, team doctors, suppliers of doping agents, scientific labs, testing authorities. They form a sealed 'cell' in terms of maintaining secrecy, enforced by the fact that they are all culpable and stand to lose jobs, endorsements, reputations... as well as being banned, having results disqualified and in some cases face criminal charges.
They have elaborate systems of avoiding detection, using the latest drug products which are always one step ahead of detection. They also have their own testing facilities and will withdraw from meets 'due to injury' if it appears they will test positive. They provide each other with essential moral support and rationale... it just evens the playing field, everyone else is doing it, i'm doing this for my family, or my country, not my self.. ad nauseum..
The only way to get control of the situation is to hold everyone that can be identified in the cell responsible for the others actions. Team disqualifications.. but also sanctions against coaches, sports federations, professional and criminal sanctions against suppliers and doctors.. .Even national associations should be sanctioned if they fail to aggressively prevent doping. They are all responsible. U.S. Track and Field has been particularly notorious in fudging its testing enforcement.
It takes money to support a doping program which means that the most egregious cheating occurs in the highly payed, high profile sports. Ben Johnston, in a recent interview stated he suspects that the 100M dash is still riddled with cheaters, 20 years after his disgrace. Some think its possible that no one has raced sub 9.90 (or more) clean in the history of the event. I will be watching that event, the related relays.. and a lot of others.. especially in athletics.. with a healthy skepticism that i'm watching a clean competition.