Put a catapult on a paracer, bring a high health turtle (carbomemys), whistle attack with the turtle and when the crab hits it put it in passive so you can easily aim and hit him on the body. No weird engineering needed.
I understand that all the previous tips submitted were useful, but just in case it was not clear, hit the TOP OF THE CRAB, it will have a special animation if you hit it in the correct spot, and will take only a small amount of boulders to tame, even a high level. (Irrelevant with Cannons)
No one seems to have mentioned that karkinos can use tools, they just need a special type of tool: doedicurus, use a karkinos to pick up a tamed armadillo and walk around to rocks and the armadillo hits the rocks and keeps them stored, argies and quetz can do it to but they can only hold one and they don't spawn on abberation, not sure but if you transfer a beaver to abberation you might be able to use it and an armadillo at the same time to gather both rock and wood
When playing aberration I found that these guys are a good rock drake egg thief. The can jump and are immune to the radiation. They are great fighters so I recommend you use these guys as a rock drake thief 👍👍👍
If you're carrying a tamed Doedicurus in your claw the Doedic will automatically start harvesting any stones you hover him over. Just start pumping points into your Doedic's weight because it will stop at about half of its own carry weight. I've yet to discover another tame it will work with though...
Be careful when carrying a Dino that has a tribe mate mounted on it. I was walking up a hill carrying my anky with a tribe mate on it and they went under the map and died. RIP ANKY AND SHINEHORN. Tribemate was eh anyway.