EPDM rubber which stands for ethylene propylene diene monomer is one of the best pond liner materials that is safe for fish. It is appropriate for a wide range of temperatures, it is flexible and will conform well to irregular pond shapes, it is stable upon exposure to UV light, and it is highly resistant to punctures. Despite that resistance, EPDM can be punctured. The very best way to repair pond liner is to keep it from being punctured in the first place. For this reason, the use of non-woven geotextile underlayment is highly recommended for all pond liners, regardless of brand name or liner composition. The underlayment is puncture-resistant and adds another layer of strong protection between the pond liner and sharp rocks, probing roots, and the gnawing teeth of burrowing rodents. If a puncture does occur, the entire liner need not be replaced. A pond liner repair kit that is specially formulated for the liner material can save a great deal of time, effort and expense.