Using rock to form the edges and boundaries of informal pools is one of the most creative (and ancient) techniques in water gardening. Each single rock adds to the overall impression and feel, so be sure to take special care when designing and positioning your rock borders.
That said, the goal is to create a natural feel and look, so don’t endlessly obsess over the positioning and arrangement of every single stone or element. When nature creates rock pools and ponds, the process is necessarily haphazard and random, so don’t feel too constrained when selecting and placing materials.
Take special care with your choice of edging, as good planning can eliminate a lot of unsightly problems later on. If your pool or pond is small and in a sunny area, be prepared for the water level to drop rapidly in warm sumemr months, which may cause the liner to be exposed if you haven’t prepared for this. The same holds true for water features that supply solely on natural rainfall and water, as the water level can fluctuate dramatically thoughout the seasons.
As far as materials for constructing a rock pool or pond, the sky is the limit, as limestone, slate, granite, sandstone, and washed boulders and cobbles all are great choices, and can be incorporated into a variety of designs in many different ways.
