Was thinking about this while picking up rocks, have to think of something!
It would take work and some time, but another way to make a stone covering would be to take any of the plastic fencing that the hardware stores sell, like the green stuff, or the black rabbit fencing. Drape it over the top of the wall and down into the water as low as you need to go.
Use your rock cap to anchor, or drape over even further and anchor in the ground via stakes, dirt etc. Take heavy fishing line, use it to attach the rocks, ie like two edges, then if need be squirt some pond foam in.
Use different sizes shapes of the rocks and put them close together. Probably keep with smallish rocks.