Another thought is you get some small pieces of acrylic (like 8 x 10) and attach it to the inside on each side of the corner that he uses as the toilet area. That way the urine will be deflected down inside the cage. I just use small binder clips to attach the acrylic to the cage wire.
Also, I don't know if your rabbit is neutered. If not, that could make a diference as to whether or not he chews or trashes things in his cage. Also, how large is your cage and does it have a wire floor?
This will take you to photos of my rabbit, Tyler, and his cage and pen