Why are you/they pro liner? My pond is 4+acres and that seems expensive as hell. Also, are the better than swimming pool liners because they suck?
Up here, the country boy way of getting a pond ready for water retainment is just a simple matter of raising hogs fenced in within the area you intend to hold water. The hogs root around in, wallow in, and just pack the ground naturally. But we have lots of clay in our soil, not sandy loam. Takes at least a year of this sort of thing to get the ground packed, though. I'm sure this wouldn't be practical for a 4 acre pond, but it might be more practical than a liner for 4 acres? I know this works in small pond applications.