Wow, second time trying to post this.
Anyway, years ago when I was little my dad brought home a large* bullfrog he caught. My brother cristened him Tad and we set him up in a 20long. After keeping him for three years, we let him go back to nature in our lake up north. Over such time his enclosure was as follows:
1. 3/4 shallow water, 1/4 dry gravel
2. 1/2 peatmoss, 1/2 water dish
3. 1/4 shallow water, 1/2 deep water, 1/4 supported dry gravel
The water was never heated and only minimally filtered. I must adimt as a young boy I was less responsible and water changes were not a regular thing. Amazingly Tad showed no ill effects. A part of every land area was a rock cave where he could be found most of the day. Such an animal makes quite the interesting pet, my entire family loved hearing him croak three times around 10:30 each night. It was even better when he'd croak along with your conversation, no joke.
While he would eat anything in sight, at times his enclosure was shared by up to three more occupents, and canibalisim was never a problem. The only death was caused (accidentally) because while trying to mate with a female, Tad held her under water to long.
*I said large before beacause he was the largest frog I had seen at the time. Yet both the Mitchell Park Domes and the Shedd Aquarium house monstorous bullfrogs two or three times larger than Tad in there collections. Quite the sight to see! Hope this all has helped, good luck ~ Rex