I have my first viv up and going strong, just waiting on good weather to order frogs. But I find my self already planning my next tank, I would like to create one that has a "river" running the length of the land portion into a large water feature(probably 1/4 to 1/3 the available base area). I was planning on setting it up as a false bottom under the land and leaving the water portion open to the base other than gravel substrate and sectioning it off with screening. Now my question is what does anyone suggest I use to construct the river bed? I was thinging a scrap piece of pvc pond liner with river rock siliconed to it, but I was wondering if anyone else had any suggestion?