A lot of people don't like getting their butt wet by sitting on a wet bench. For these people I give a piece of advice: stand. But for those who absolutely must rest their legs there's the Rolling Bench. It's a wooden slat bench that can be turned via crank to expose the dry underside. You can use it to crank bums and/or old ladies off the bench as well. While a novel concept, I imagine they'd be expensive. And it's not like a wet bench is that big a deal in the first place. Just do what I do and sit on a stranger's lap. If it makes them uncomfortable you know you've found a good spot. It's when they invite you to sit on their lap that you have to be careful.
Wet Benches Suck [electroplankton]
Thanks to Nils, whose IQ rivals that of Einstein, for the tip