That would be an awfully hard thing to do and it is a little far-fetched to be taken seriously as a flaw with the argument. It's far more likely that many players are deliberately orchestrating situations like Santana's where they dope up knowing they won't be tested in order to cash in big time at the expense of their team and other players. I think one of the things that might help avoid the unlikely situation you're talking about, though, is more frequent testing. If players are tested more frequently by independent agencies they'll be better able to narrow the window in which their test was dirty, thereby allowing them to raise a grievance if they think there was some Belicheckian plot with a towel guy in the weight room. And, going further, even if there was a sudden pile of aging, bad contract guys magically testing positive - that would raise the red flag the other direction. But right now that's not the problem, the problem is we have guys knowingly cheating their way into contracts that hurt the teams they sign with. There needs to be something teams can do to counter that to punish those offenders.