All I can say is I am kicking myself for not putting down a pad when I replaced my liner 3 years ago. I had sand, and I decided to stay with it. I re-leveled it, packed it, smoothed it, and was extremely patient going over it.
It is now a bunch of small divots, and I can quickly point out to you the two small rocks under the liner that I watch like a hawk for leaks. Next time, I am using a pad.