I appreciate the concern, and I might have to rethink the setup if i keep him permanently. I'm still trying to decide if I really want to keep him or not, but I have been having a lot of fun setting up the tank and learning about these guys.
However, I will say that I've been browsing the forum posts, and many people seem to keep these frogs in ten gallon tanks. I have a twenty high, with less than half the tank filled, which is taller than a ten gallon. There are many spots throughout the tank that would allow the frog a grip if he did fall in the water, which he has once or twice. He didn't seem to have any difficulties getting out of the water.