No matter - I've now bought a proper liner and underlay off eBay for about £10, and I've been reading up online about how to build a frog pond properly. I had visions of having to dig half way to the Earth's core, but apparently 25cms is perfect for the deepest point and gently sloping sides all round are supposed to be best as tadpoles like swimming about in warm shallows.
The liner will be longer than the plastic I've used, but that's ok as I can easily lift everything out of the way and re-dig the pond a little, as there's plenty of room anyway. This time, I'll use a spirit level and not trust my eyes - as my attempt at creating level edges was two inches off.
The shape of pond-to-come.
Pond Attempt #1 - a bit leaky, but it already has one frog...
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