I kept my motoros in ponds made from 45 mil Firestone liner. Every year I would find a leak and had to replace the liner. The rays either poked or chewed a hole in it every year. It was a real pain to replace (remove the rays, shut down the filter, remove the sand, take apart the top of the pond, pull the liner, etc.).
If I were to do another ray pond, the interior would have to be of solid construction (fiberglass, tile, etc.).
Good luck,
Colin