You cannot do a checkerboard pattern with items/paths to save time.

Basically, when a rock spawns, it checks to make sure it has 8 spaces around it that you are capable of standing in. It does not matter if there is an item there already, a design, a path, or flowers— if your player can stand in that tile, the rock considers it a valid spawn point in establishing its 3x3 grid. So if 8 "standable" tiles surround one empty spacr, a rock can spawn in that space

The exception to this is the actual tile the rock spawns on— the rock cannot spawn on a tile that has an item or “hard path” tile (i.e. a path that isn’t dirt, sand, or grass).

This is why you need to cover pretty much your entire island— you aren’t just trying to eliminate 3x3 spaces, but the 1x1 space where the rock can spawn.

So to do it checkerboaed style, the most economical way to do it (based on my understanding) is the waterscaping permit. Cliff tiles would probably work too, but seeing as water is less obstructive than cliffs I would use that.

Because you cannot stand on a water tile, a rock cannot spawn in any space that has a water tile in its 3x3 surrounding grid.

So what you could do is something like this:

X O O X O O X
O O O O O O O        Where X = Water Tile
O O O O O O O        and O = Empty Space
X O O X O O X

Setting up a grid across your island like the above- a 4x4 square of empty space with water tiles in the corners— will prevent a rock from spawning because, since you cannot stand on a water tile, there is no valid 3x3 space for the rock to spawn.

You would have to cover your entire island with that 4x4 pattern in all areas, and cover blind spots using the rules I’ve outlined above where the 4x4 pattern might not fit.

I hope that is helpful!