It is a good idea to use an underlay under any lined pond to prevent punctures and leaks from developing. Do not cut corners here because if your liner leaks you will need to tear your pond apart and start over. Commercial underlays are now available but in the past sand, old carpet, felt, or even polyethylene bags have been used.
It’s not a cheap option but when I built my pond I bought a purpose built underlay for ponds something like this.
http://www.underwaterwarehouse.com/prod276.html
The stuff I got was also made to stop tree roughs growing through it .
It’s not a cheap option but when I built my pond I bought a purpose built underlay for ponds something like this.
http://www.underwaterwarehouse.com/prod276.html
The stuff I got was also made to stop tree roughs growing through it .
