We've had good luck for years with our black tarp winter cover, but this winter's heavy snow, and last summers mice in the shed, tore it to bits. How do I measure for a new one? Out pool is 16'x36' with a 8'x8' L section. So basically we need at least 24'x36' of coverage. What size tarp (and thickness) should I get? What are some good online sources? Thanks, Ed