what ever you do, if your going to go with foam back ground covered in concrete or anything of the such, consider the economy of motion and don't over do it. also, don't paint cement. there are many types of pigments that are permanant
and most concrete expoy or acrylic sealers will crack and flake
off! it's not recommended to do the above mention approach.
you can either build it with the land encased in you cement - vivarium mortar or like in these example, enclose the water feature. both have their good points but, make sure your sealer is either going to soak in like ours or it's not used. chips can get an animal hurt, don't look good and yellow. don't paint, use pigments or dies or acid stain. Lower the pH of your work! portland or plastic cement are high!!!
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close up of drained palidarium - 3' x 2' x 14"d