I re-use disposible swim nappies.
I know I have used one at least 5 times so far - just washed it in water after swimming and dried it on the airer/radiator. I even accidentally put one through the washing machine and tumble dryer once and it came out looking fine
(I'm pretty sure they don't contain any gel or anything like normal sposies).
I have thought about usind a pocket but can't help worrying about all the chlorine in the pool damaging it.