Liner, underlayment, and geotextile are the pond's foundation. Choosing an inferior liner can lead to a leaky pond. Educate yourself on the selection of liners that are available. Don't consider using a liner if it doesn't come with a long-term warranty. It is important to also determine whether the liner you choose is safe for any fish that may inhabit the pond. Underlayment is installed before the liner in order to prevent punctures that may occur from rough or rocky ground. The underlayment actually serves a couple of purposes. It not only provides protection for the liner against rocky soils and roots, but it allows the ground to breathe from underneath. The earth releases gases and the fabric allows the gases to escape from underneath the liner rather than becoming trapped, causing gas bubbles to push the liner up into the pond.