dividing a terrarium for a pond
I'm on an assignment. My wife has a glass aqauarium in which she keeps four tree frogs. She's spent months playing with various fountains and pumps to create a waterfall and finally has what she likes. It sits in about 4" of water at the bottom of the aquarium so the only dry land that remains is what she's created on rocks and plants. She wants me to add a 6" high divider so she can keep one end of the aquarium dry with a pool at the other end with the waterfall fountain. She's even brought me a tube of aquarium silicon to use.
Rather than glass, I thought that polycarbonate (lexan) or acrylic (plexiglass) would be safer and easier to work with. Are either of these materials particularly good or bad for this purpose? How thick would you recommend?
Are there other ways to create a pond? I thought about using pond liner and small stones, but most pond liner is pretty thick to form into a small pool like this. I don't want to create a lot of work for her to rebuild the pond each time she cleans out the terrarium. Can I glue the stones in place and will they stay put with silicon?
Thanks for any advice or ideas you can offer.