Is there a way to anchor a bone so when I move my root bone, all bone move using IK except the anchored bone? This would be super useful for trying to make a squatting pose where I’d anchor the feet, then move the root bone down without the feet moving down as well.
It’s usually best to have a detached root bone at the floor level. Parent the leg IK targets to this and you’ll be able to drop the hips without the feet moving, resulting in a natural crouch.
Lock the Stiffness Items in the Bone’s IK sub pane as below:
Just click the locks. Alternatively you can set the length of the IK chain (it is 0 by default meaning full length of all connected bones), so the last bone in not included in the chain (if this is the 6th in the chain, set the chain length to 5 in the IK constraint itself).
Cheers, Clock.
Stiffness will not have any affect on what thundercleez is asking for. Stiff knees will not prevent the IK target from moving. The problem he is describing is the result of his IK target bones being children of a root bone that is most likely in the hip or lower spine area of the character. The hips should generally be the root bone of the rest of the main skeleton, but what is needed here is another higher level parent bone that holds the hips and the ik targets, so that the latter may be moved independently of the former. Stiffness may help direct the motion of the knees when bending but will not help with the location of the feet, which is the more relevant concern.
Point taken - today I have learn’t something, I normally would lock the three axes on a bone in the Ik chain that I did not want to move, e.g. cylinders on a steam engine. I seem to have got the wrong end of the stick here. Sorry to confuse!
Cheers. Clock.
You’re thinking too high in the chain. No matter how stiff the shin bone is the feet will still pass below the level of the floor if the IK target does so. If the target is a child of the hips, it will move when the hips move. To get a crouch pose, the feet (and thus the IK targets) must remain in situ while the hips move downward. If you only stiffen the knees, then the legs will simply remain straight while the legs pass through the floor, an identical result to the existing problem without stiff knees. Stiffness is not only irrelevant, but in fact will create the same problem all over again with a new cause.
It’s a bad day when you don’t learn anything new. 
Yep got it, i was not talking about stiffening the knees, more removing the top level bone (that furthest from the bone with the IK Constraint) from being affected by the IK chain - this is just what I did for someone else in the rig below:
ik-chains.blend (453 KB) Thanks again for your input. Clock.