Goldfish

Currently building a 43,500 gallon koi n goldfish rec pond and yes i have dug the entire thing with just a shovel and a wheelbarrow.....Dimensions are 25 ft wide 40 ft long and from 2 to 6 feet deep.....Does anyone have any recs for a good liner for my pond?? If by chance anyone in central indiana is looking to rehome some Koi ill have a home for many sizes.