Thanks. I got the underlay from Pondsonline. I'm pretty sure it's 10oz. It's very thick. Same stuff they use on roads. I got 15x300 feet and that would pretty much cover my whole "beach" area. I did also get the landscape "nails". I'm thinking that putting the liner in the part of the pond where the plants will be, will be sort of a waste.

That's good to hear you don't have many issues with the rocks sliding, even on the 3:1 slope. What kind/size of rocks did you use?