We used an old tyre, having first cut off the rim on one side. The trye gives the pond strength and stability and also gives another level inside the pond. The hole was dug 38cm deep (min) the width of the inside of the tyre, levelling out at the top to the width of the outside of the tyre so that the tyre sits flush with the surrounding earth. In the hole place some fatty sand or thick layers of newspaper. This protects the liner. Make sure everything is level and then add the liner, (we used 2 pieces of builders plastic). Fill with the hose making sure you even out pleats as it fills. When water is at the top of the inner hole place the tyre on the ledge, placing the piece you cut off underneath ( this disposes of it ). Finish filling the pond and when it's full place a stick in the pond, making sure it sits inside the tyre so that you don't pierce the liner, for lizards and birds. Over the rim of the tyre place some rocks to hide the tyre but also for habitat for beneficials, being careful not to push down on the rim.
One of our participants was a mother of a toddler with another on the way. She was a little concerned about the safety of the pond with children around and asked if there was another way to attract frogs. ..
There are many frogs which don't like deep water and will live in and around shallow water and make themselves quite at home in bromiliads.