Another question.........sorrrrrrrry

I know we are supposed to remove all rocks/stones but that is 95% of our soil I think. There are literally thousands of rocks/stones. So I was wondering if we could use 2" styrofoam between the earth and sand? Would this work? I hadn't planned on buying "Happy Bottom" or anything like that to go over the sand though. What about wall foam? Does everyone use wall foam? I think I am going to buy the cove instead of building it out of sand just to save my hubby some extra work. Thoughts? Thanks so much and sorry for all of the questions!

Dena