Building in Sandy Soil

[myswtsins]

I live in a sandy/loamy soil area, great for digging but we are worried about wall/edge strength. We plan to do 2.75ft near vertical walls through out most of the pond with a few shelves on one end, for stairs mostly and no rocks in the pond besides the edge rocks. Any precautions we should take? Was thinking a concrete collar under the rocks on the lip will help that edge, should we be concerned about the walls themselves? Thanks in advance.