Excavate the pool to desired shape, incorporating a marginal shelf at a depth of 20cm for plants that enjoy shallow water. Ensure the walls are at a slight angle of 10 or 20 degrees. Continue digging until you have the desired depth, normally between 20 - 24 inches (50 -60cm). Check that the hole is level using a plank and a spirit level

Lay strips of underlay to provide cushioning for the liner. Drape the liner loosely into the hole so that it just touches the bottom of the hole in the middle, making sure that there is an overhang all round of at least 25cm (8"). Anchor the edges of the liner with stones.

Start to fill the pond - the weight of the water will form the liner into the excavated shape. As the pond fills, begin to fold excess liner and allow the water to mould it to the sides. Keep moving the anchor stones to allow the liner to feed into the hole. It is a good idea as you begin to fill the pond to establish an accurate measure of the pond's volume. The easiest way to achieve this is to time how long it takes to fill, say, a two gallon watering can. Then time how long it takes to fill your pond. If for example it takes one minute to fill the watering can and one hour thirty minutes to fill the pond then your pond volume will be 2 x 90 = 180 gallons.