Pond edging is one of the most import aspects you need to think about when designing your, pond because how you are going to do this can effect the whole digging process. There are many methods of adding an edge around your pond and the method you use will largely depend on the pond construction and its location in you garden. Here are a few ideas but there are many many more and you can also use ideas from each of the below ideas in one pond.
Pond edging ideas using various types of material
Use rocks to edge pond and hold down the lining.
Use paving slab to edge the pond and hold the lining down. If using mortar to hold slabs together try not to get any in the pond water
Use vertical paving slab to edge the pond and hold the lining down. Fold lining over the slab and then put soil up to the lining to hold it in place.
Use marginal pants to edge the pond and hold the lining down