Waterproof masonry, such as concrete, is ideal for water features as it seal in the water, whether it is a raised or sunken pool. If you are choosing a material with joints, such a brick or rocks, they will leak so you should add a specialized render to the interior of the pond. You can choose colored or clad with tiles or a waterproof membrane such as PVC. Do not add any decoration, made of material, which can puncture or damage the waterproof liner. In addition, the joints where pipes enter the pool should be watertight. You can line the edge of a pond liner with flat stones will protect it, but it needs to be smooth-edged to prevent punctures. Natural stone has been used for hundreds of years to build water features, especially fountains. And when it comes to natural look, nothing beats it. You can use sandstone or marble, which are available in variety of colors and patterns. Granite is a very strong and natural material.