GeoGuard, a felt type product that is almost as puncture proof as it is thick, provides a protective layer between your swimming pool's liner and its sand or soil base and is designed to provide tremendous strength while providing comfort for your tired and aching feet. Because it's pre-cut to all standard pool sizes, GeoGuard is easy to install. GeoGuard's geo-textile material, resistant to all acids, alkalis, salt, and oils, prevents cuts and punctures to the vinyl liner caused by rocks, glass, roots and the highly invasive Cyperus rotundus, your pool liner's greatest enemy.