How do I rotate a bone without effecting the connected bones? I've been looking for answers to this problem, but I'm too much of a newbie with rigging to understand some of your answers.

So here's the thing: I'm trying to modelize and animate steelix:


Considering his snake-like shape, he's not so hard to rig and animate, and this is what I made:


But here's the problem: Steelix's spiked boulders can rotate on themselves, and with this rigging, whenever I rotate a bone, the whole body parts connected to this bone also rotates.

What should I do to make that the boulders rotate only on themselves?
Go into Bone Edit Mode of the Armature. Tab
Select the spiked_boulder bone and duplicate it. ShiftD
For further convenience, let's scale this bone down, so we can discern it later on. Let's name it spiked_boulder_rotation.
Parent spiked_boulder_rotation to spiked_boulder. CtrlP
Assign/Parent the spiked boulder mesh to the spiked_boulder_rotation bone.


Now you can animate the movement of the spine in a standard fashion. The child spiked_boulder_rotation will rotate along its parent moving the geometry. Now animated the Y Rotation of the spiked_boulder_rotation if you want to additionally rotate the spike geo.