We're working on a project that includes a pond. Our Aquascapes kit is on it's way, and I'm wondering about using the underlayment on top of the liner. The look we're shooting for is to have a small retaining wall (2' tall x 15' long) of natural stone (top stone will be 200# outcropping stones) with a waterfall spilling from the middle. While there shouldn't be any razor-sharp edges, I'm still concerned. Can I use the underlayment on top of the liner? Some of it will be exposed to water constantly, so I wonder about it breaking down in a couple years.