I'm not too hot on the name but anyway. The theme of the feat is that I believe that a monk should be a viable tank character.
Martial Defense
Prerequisites: Monk level 6, Combat Expertise, 13-15+ wisdom
Effect: While this feat is active while you are centered and in Combat Expertise mode you are treated as if you had a light shield equipped for threat generation and feat purposes. If this results in DR from shield mastery feats your attack speed suffers by the same amount as your damage resistance (not counting the bonus from improved shield mastery).
Complimentary enhancement line:
Improved Martial Defense I
Cost: 4 AP
Prerequisite: level 10 monk, x number of AP spent
Effect: heavy shield instead of light shield (activatable).
Improved Martial Defense II
Cost: 6 AP
Prerequisite: level 14 monk, x number of AP spent
Effect: tower shield instead of light shield (activatable).
Overall I think this would be a neat way to give some more diversity to the monk class without being OP as you would have to take shield mastery feats still to be a viable tank.
Edit: made adjustments considering feedback in this thread.