My solution would be to allow doping, but that declarations must be made. If a drugs athlete comes 1st, 2nd.3rd, then another medal is awarded to the first non-drugs athlete as well. Anyone claiming to be clean, but is actually doping is given a life ban from all sports, no exceptions.
There's then no incentive to not declare, as you can openly dope and still win a medal. Equally, if you aren't taking drugs, you can win on a fair playing field - plus, you have the opportunity to beat doping athletes.