I think all of the primary bases are covered that I know of. But have you thought about vines or a plant either on the wall or against it. A couple of vines or tall bushes against the wall would help to cover it. Rock roses do very well in warm sunny areas just growing out of a big pot, or even out of a planter hanging down. It will take a couple of years to fill in, but I think growing plants would be the cheapest direction.
If this is a retaining wall, I am also a little concerned about attaching any screws to the wall to securely attach any weighty rock solution.