As the Ricco situation makes clear, the dopers will always be looking for the next new non detectible drug. And the nature of the game makes it likely that the dopers will always be a step ahead of the testers.
However its difficult to believe that there could be significant doping on a 3 week grand tour, without fellow riders, support staff, and directors knowing about it. You just can't travel,and live in that close of proximity for 3 weeks without people picking up on things IF THEY HAVE THE INCENTIVE TO BE LOOKING.
The Team Organizers, and fellow riders are the people in the position to stop this. The rules need to give them the incentive to do so.
Until and unless Team Management feels the pain this sh*t will continue.