Of the 33 rocks standing in the water, 28 now carry authored resting spots — alternate patches of the same seabed the rock has always stood on, never a reshuffle across the map. Thirteen carry five spots, eight carry four, three carry three, and four carry two. One rock has no safe second spot at all and always reforms exactly where it broke — a real gap in that stretch of water, not an oversight.
The four rocks that hide a Pearl shell don't roll a spot of their own — they move with their shell instead, holding the same offset from wherever that shell's own resting spot lands. Break one, wait the fifteen minutes, and the rock reforms guarding the shell on its new spot, not its old one. See A prised shell comes back somewhere else.
The same three guarantees carry over from the shell. A rock you've never broken never moves. A rock mid-countdown never moves either — it settles only at the instant it reforms, never partway through the wait. Closing the game, reloading, or coming back tomorrow reshuffles nothing: a save remembers exactly the layout you last saw. And every candidate spot was checked before it shipped — none of them can bury a pickup, a landmark, or a passage, or sit close enough to another rock to trap the drone. Full mechanics in the guide: Hazards, Wear & Repair.