Once you’re satisfied with the fit, start to fill the liner with water from a garden hose and continue to make sure the liner is sitting level as it fills. If you notice any puckers in the liner, you’ll need to backfill with some of the dirt you removed to fill any air pockets (you can also use some sand). This is especially important underneath any shelves as you don’t want the liner to buckle under the pressure of the water – the liner needs solid support, both underneath and all around the sides!
When the liner is filled about halfway with water, backfill around all the edges with sand. We used a plastic hand trowel to direct the sand where we wanted it. A deep dustpan works well for this purpose too – place it away from the gap between the side wall and the liner (under the lip), then brush the sand into the gap to fill up the sides and secure it all around the edges.
We purchased some flagstone to hide the edges and finish it off (a few pictures follow in the next section).
When we first installed our liner it was with the recognition that one day we would be installing new paving stones. We actually ended up doubling our work because of that; we had to re-support the pond when we updated the walkway. This is how the walkway looked before we installed the new pavers. As you can see the liner is level and sits on top of the stone slab.