Slate is an excellent choice for use around a pond border. Not only does this material weigh enough to remain in place, but its natural colouring blends well with the water as well as the surrounding vegetation. Choose large, heavy pieces of slate for use on the pond border to ensure that the rock does not shift and that it cannot be easily dislodged.
Add dirt to the edge of the pond with the shovel so that the area where the slate will be laid is flat and level. Pat down the soil, and ensure that the slate will not rock or shift when placed at the edge of the pond.
Place the slate stone around the pond. Choose pieces that fit well together, forming a tight gap between neighbouring stones. The stones should overlap the edge of the pond by at least 2 inches to help hide the top edge of the pond liner.
Bury the slate furthest from the pond edge under a few inches of dirt. Work the dirt into the crevasses between the rocks, and smooth out the outer perimeter of dirt. This will allow some vegetation to grow on the stone, producing a more natural appearance.