I am planning a "stream-leading-to-pond" in an area behind a retaining wall in sloping, very sandy conditions. Like making a stream and pond on a sand dune. My plan is to super saturate the soil with water to make it stay put while I dig out the forms for the top resivour, stream and pond. My biggest concern is the easily shifting soil and was just wondering if anyone has any experience in working with that environment. I guess my question is how to keep the sand from shifting once the basic liner and rock are in place. Rocks? Concrete ? Topsoil ? Lots of vegetation?