HOW TO STOP THEM: u can either build some sort of cage u trap them in, or u make them get stuck between some big rocks while they are chasing u;
HOW THO KNOCK THEM OUT: u can place a CANNON (most Torpo if HEADSHOT -> u will see them shake their head if u hit the right spot -> animation!) on a paracer (first platform&foundation) and then try shooting them while they chase u -> big ammo waste as if u will not hit them while moving!; best way is to trap them, so u can even place a stationaire cannon next to the cage/trap wich makes it easier to releoad and store cannonballs directly next to the cannon, but still be aware of thrown boulders by the elemtal as they do a lot of damage -> build some kind of defense wall to avoid getting hit!
now with the right aimed cannon (i suggest at leats 3 walls of hight to place them) and the right timing u should knock them out pretty easy...
It's a bit silly that kibble tames it a lot better than rocks or sulfur because even in the dossier it says that it lives off of absorbing nearby rocks and minerals. So mabey they should make it so you have to feed them a rare mineral like obsidian what if they made it so you could tame one fast and with high effectiveness by giving one a few hundred or few thousand obsidian . or what if there kibble was made out of a combination of ores and minerals .