I just bought a fiberglass pond, approx. 250 gallons, and would like to set it on my concrete patio in the backyard. The concrete is not level in some areas though. How do I support the pond so that the fiberglass doesn't crack under the weight of the water? I plan to put potted plants around it and build a bench to look at the fish. Would leveling sand work or would it wash away in the rain? If you have ideas, please let me know.

Thanks for your input!