10 whacks from a no star Fuling is enough to destroy a section of stake wall (and allow them entry), Growths can jump over a stake wall. Stone walls have 50% more durability to damage than stake walls no matter what size pieces of stone wall you use. If you interlock 2x1 stone wall sections it will take a Fuling 15 whacks to break that wall section but to get inside a Fuling would have to break through 2 of those wall sections.

Earthen walls require rocks, a hoe, and a work bench (instead of a stone cutter) to build and earthen walls are invulnerable to damage. They can also be raised high enough (8 meters from base terrain) that blobs and growths can't jump over them (but other flying creatures can still fly over them).

You don't have to worry about conserving rocks, they are literally all over the place in every biome. You'll get more than enough rocks to build any thing you want just from mining copper and silver and Graydwarves drop them so even if you were to mine every single rock (and flatten every mountain) on your map you would still have an unending supply of rocks.