I'm replacing an existing 20'x40' inground pool that has slightly caved-in. The existing Shelves (dirt Shelves) look to be in decent condition/elevation for the new Pool Walls--but what if there are areas that have caved-in below the 40" wall shelf elevation? Do you build them back up with stone to get to the 40" elevation? I really didn't even want to rebuild to this size--but several pool companies I spoke with said it would be easier to build on the original footprint in order to use the existing Pool Shelves. Just want to be prepared in case we run into areas where they may have eroded past the 40" for the new walls.