Adding rocks to a pond means more than just dumping some gravel across the bottom. For a truly natural looking rock lined pond, your job starts at the edges. Collect larger rocks for the border along the edge of the water that covers the liner. This rock border also protects the bank from erosion and allows wildlife plenty of places to hide and get close to the water for a drink. As you complete the edges, continue laying smaller rocks along the sloping slides and larger rocks along the bottom. You can add gravel if you like to reduce the amount of large rock you must buy to complete the sides and bottoms of the pond.
Look for smoother slabs and chunks of rock rather than sharped edged pieces. Sharp edges wear away at the liner over time and can cause tears. While sharp edged rocks fit together tightly for easy stacking, they’re better for a wall built on land rather than stones covering a pond liner.