Fire Belly habitat

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I've had my frogs since about march/april 2010, and so far they are the coolest pets i've ever owned (and the only ones!) and i recently got them (4 of em) and was wondering if i could get some pointers. in the tank right now, i believe it is a 20 gallon tank, and i have about 2/3 of the place is water, and then i put a divider and made a land portion for feeding. i was wondering if my water is too deep, it sits at about 3 inches (see pictures). i guess what i want is suggestions for their habitat. and also on a side note, i've been reading about how they don't normally go under water, but mine dive down under some of the rocks, and sit there for a pretty long time. any ideas?