There is actually another design, but they are incredibly hard to find. BA105 - Rear Lamp Guards for Discovery 1 | LR Parts
That said, I really don't see the point to ANY light guards. Any guard tough enough to protect the light will have to be securely mounted to the body, which means when a branch or rock grabs it you will be left with bad body damage. Any guard that is designed to "give way" when something catches it won't provide adequate protection to the light its attempting to guard.
IME no light protection is the way to go. Over the years I've gathered probably a half dozen rear lights and just put them in a box. I haven't needed them yet, though. Even when I dragged the side of my truck along a washed out bank it didn't hurt the light. The whole side was trashed and the rear passenger side corner was separated at the seam to the quarter panel, but the light was unharmed.