I decided to restack the rock today. I moved the large rock in the center to open up the "cave." I created more caves in the process. I think I finally like the rock work. It is hard to get the feeling of depth in the picture, but the opening in the center goes back almost the full 24" of the width of the tank.
It is now essentially two tall "islands" connected by the arch, with some rock stacked against the back wall.
