Your only defense is to not bowl the tournaments that let him do it. Or at least don't get into the brackets. The brackets is why tournaments let the idiots continue to do it. If you are running a tournament and the guy buys into 50-100 brackets, and you make $5 per bracket, then you can get nearsighted real quick.
We have a tournament series around here called MAMBO and they have a couple of guys who bowl pretty much every squad and load up on the brackets, side pots etc. Everyone knows who the cheaters are, but nothing is done. Needless to say, I don't bowl MAMBO any more.