Good idea on larger rocks over the gravel. Gravel is fine under the water. Could make a GS foam bottom with a pond?
When I make his permenant home ill be doing something along those lines, with a large water area with live water plants, water fall and wood to climb out on. And also a land section to use mostly for feeding.
2.0 Bombina orientalis
1.0 Bufo americanus
0.1.1 Ceratophrys cranwelli
0.1 Xenopus laevis
All my arachnids and other inverts listed in my profile