I remember an incident at Parx many years ago where it was rumored that trainer Sal Campo was putting over a first time starter in a maiden claiming race, a horse that should have been running in a Maiden Special where it really belonged. However, loose lips sunk ships and another trainer dropped a claim slip on the good thing. Campo got wind of this, and used a prearranged signal to alert the jockey in the post parade. Once he was far enough away from the outriders, the jockey jumped off during the warmups, the horse ran off (FAST), and was scratched from the race. Betting coup was foiled, but at least the trainer didn't lose the horse.
Not a peep was heard from the slumbering stewards...........