Why - you look at the approved plans, of course!
Alas, 'tis true...most pool decks are not 4" cover



. So the PVC for the pool light needs to be at the proper burial depth. This is one of the most flagrant violations that electrical inspectors (I like to think unknowingly) allow, here in our state.
Not to mention the fact that most PVC runs for pool lighting do not even begin in a deck area, but rather some part of the yard, and then continue on into the deck.
So have fun, and catch these burial depth violations!