It is a simple and straightforward task to add a ridgid liner to the garden, but there are other considerations when the liner is going to be up against the edge of a walkway (as ours was). We ran into several challenges.
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.