I made a protector for my 8x10 a few years ago by cutting a piece of scrap 1/8" mahogany plywood ("lauan" or 1/8" "door skin") to the appropriate size and shape with a kraft knife and gluing a piece of felt to the side that faced the glass. I put 4 small pieces of Velcro on it and the frame that holds the glass to hold it in place. Total cost about $2.00.