I would be cautious about drilling holes in the metal frame. I had a set of household swivel rockers that I returned after they bent within a week. Yes my kids were spinning on them, but I would be worried about compromising the strength of the frame and making a weak spot. I would think clamps may work to lock the mechanism in place, but I agree pics would help figure that out.
D.E.Bishop wrote:
To the OP, there is probably a simple way of doing that but...
Two or three clear, well focused photographs of the swivel/rocking mechanism wold help. I would need to see the chair and mechanism (pictures) but I do not think there is a really simple way of locking and unlocking the movement of the mechanism. If your husband wants to permanently stop the rocking motion, it is probably as simple as drilling a hole in the mechanism and putting a hardened bolt in the hole.