I have used a tripple layered ( set of 3 the same )
blue roof tarps from the home depot .
In my pond now for 3 years , I did it as a quick thing and was going to replace it with a real black rubber pond liner but I never got around to it .
the fishare growing good . everything is cool.
I cant say anything bad about it .
Will it last 4-5-6 years I cant say
what I can say is its been great for the past 3 years
chuck.