If you are caught, your bats are confiscated. Knowing this, they will have one corked bat and the rest will be regular. If you are somehow caught, the rest of the bats will be examined to find they are not corked, so you can use the argument " I use that for BP or homerun derby and it got mixed in with the regular bats". They can't prove otherwise. To solve this problem, they should not allow a corked bat in a major league park on days of an official game, and if you are caught with one it's a season ending suspension.