It's not clear to me how the Retention Wall will look once both the upper and lower West Lawn areas are finished and all the plants are in place. But it might be nice to soften it by some plants. Maybe something that runs along the top of the wall, and cascades down it.
So I planted a Wooly Stemodia ($6.99 from Barton Springs Nursery) at the top of the Retention Wall.
It is perennial, semi-evergreen, low moisture. The main issue will be that is likes full to partial sun. In this spot, it should get sun in the morning, but in the afternoon it will be shaded by the big Oak tree, and the Jungle and Bamboo Grove. We'll see how it does here.
Follow-up note: Apparently it wants full sun. Over a couple of weeks, it withered and died.