I do not use sand in coop or run, it doesn't work for me.
That said, I don't understand the point of sprinkling DE/PDZ on the old sand, then burying it. If its being added for control of mites, etc, burying it just ensures its less effective and more likely to be moist, which reduces its effectiveness further. If you are thinking your birds will scratch in the new sand and "turn up" the buried DE/PDZ (probably true, to some extent), how is that any different from putting DE/PDZ on top, and letting them turn it in???
Like I said, I don't do it - but as I think about it, that's what first comes to mind.