Build a square made of pillars and take out one end of the square. Now have a freind aggro the Rock Golem into it and make the golem attack the pillars while Facing foward. Now aim the cannon straight towards the golems head and make sure your freind stays infront of the pillar to keep agro. Now when the golem stop doing his spin attack shoot the golem and he should flinch if you get a hit. It is recommended to have about 20 cannon balls to ensure you don't run out have way. Now once you have it knocked out feed it Mantis/Sulfur and make sure you pin it in as it is a very long tame.
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 .