A mini-pelle is necessary if you want any size at all and especially if like me you are digging in rock. The photos of my swimming pond are in the other thread but it is only one of 3. The largest, because it is for swimming in, is based with fine sand and carpet underlay with a thick rubber liner. Make sure the liner is much bigger than the area of the pond because it will be dragged in as it fills with water. I over compensated somewhat as can be seen by the liner all the way round still in evidence after nearly 20 years. I have resisted planting because I knew I would be clambering in and out, but it would be nice to look less bare and contrived.
The other 2 ponds are different. Neither for swimming. One is barely visible in trees and the lower one, in full sunlight has generated its own beneficial growths in and around. The drawback is that the sunlight causes rapid evaporation so in times of drought it gets very low indeed. Despite that there is much life in that one, newts, frogs, dragonflies, skimmers, water boatmen and snakes, though all are present but less visible in the others. The natural ‘weeds’ in the bottom keep the water clear, unlike the other ponds which, being in trees, collect a lot of dead leaves on the bottom and visibilty is only about 50 cms due to the algae ‘dust’ suspended in the water. I do dredge the swimming pond with a long pole net, but the middle pond is left to its own devices and I think the build up of leaves means that now it has little real depth. Perhaps it will become a natural bog one day with its own unique ecosystem and residents.
The fears of a neighbour that they would be a breeding ground for mosquitos have proved unfounded and, from non of them, does a smell arise. I, for different reasons, love all 3 of them.