I believe that this guarding is a result of a compensation for a lack of stabilization.
It is from the principle of Stability/Mobility that I developed the ARMS (Active Release with Manual Stability) release technique. The success that I have achieved using this technique in my practice, reinforces my belief that hypertonic, guarding muscles are compensating for a lack of stability elsewhere.
I was trying to mobilize the connective tissue around a sacrum so that it could move in the direction of nutation. I had tried all of the techniques that I had learned for release without success.
The words of my Orthopedics teacher in PT school "you need to have stability in order to have mobility" entered in my mind. I then provided a prolonged hold type of stabilization to the patient's abdomen and the hypertonic tissue immediately released.
Yesterday I attended a private Pilates session with a patient who I referred there. He expressed that when he was performing a certain exercise, he felt that the spasms an tightness in his back release.
To answer my colleagues question, I think that a person with muscle guarding does not gain adequate stabilization from this guarding, and teaching them stabilization exercises and techniques may in fact help to decrease their painful muscle guarding.