The rocks have been hand-placed along the vertical shelves of the pond for structural stability. Gravel covers the horzontal shelves of the pond to protect the liner from UV rays and to give beneficial bacteria lots of surface area.
DIY - Homemade Gabion wall ie rocks encased in wire baskets and used as a retaining wall - creates a dramatic feature in a garden. No directions on link. Nice someone figured out how to landscape with river rock. I swear they grow!