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.
To tame these turret soakers I’d recommend getting four metal gates 5 pillars 3 ceilings and 3 walls. For the trap and the pillars are supposed to prevent the golems rocks from hitting the cannon. AIM FOR THE HEAD