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?