Rock elementals are extremely tough to kill or knockout. Over encumbering them inside or around your base and setting them to aggressive allows them to defend your base with their rock throw attack without being kited away by enemies.
Rock Elemental can take a lot of hits reducing damage by 50% from all non-blunt damage. A TAMED Rock Elemental can NOT fight a wild one. It works the same as a Giga so I would advice against it.
they should make it so when its hurt and you put stone in it it does this cool animation where it repairs/heals itself will the the rocks rarer minerals repairs/heals itself more