Let's take the men's Marathon as an example. Every runner in the world who is currently active competing and has performed under 2:18 should for the love of the sport allow WADA to drug test and monitor them for 6 or 12 months, each single day. Whoever don't support this ultimate war on doping is a doper and permanently banned. Because if they are really clean they should happily do it since the dopers will be out and they'll win big cash prizes soon on big road running events.
This will be quite an investment but it will be worth it. By the end of 6 months We will get an emerging picture on what's the actual world class standard in distance running, how many athletes can actually run sub 2:10 etc etc. They should conduct this approach after every 4 years before the Olympic year, until they've found a better technology :D :D