I have hear or read that the width of the pond is not what you use to determine how strong to build the side wall of a pond, but the depth of the pond is what you use. I hope that makes sense, I am not an engineer. For example if you built a cement pond 40 cm deep by 10 meter wide by 20 meter long with no rebar and the pond did not leak you could, if you wanted, make the pond 50 meters wide and still use the same side walls. But if you made the pond deeper you would have to maybe make the side walls stronger. Is this correct information? How deep can one build in undisturbed soil with cement blocks filled and rendered without iron/rebar?