Epoxy all the way, your lungs and frogs will thank you! Polys are some nasty stuff!Properly cured urethane resin works well too, but it's not easily available to the average consumer. You'd have to buy it online. Epoxy is more forgiving in terms of it's ratios, curing environment, cure time, and is generally less hazardous in it's unpolymerized/reacted state. So stick with a good two part epoxy.