i have made a automatic tension wrench out of a tension wrench, self tapping screw and a large nut, here are some pictures
shows the wrench end and inside of nut with self tapping screw
http://tinypic.com/kvxmr
shows the screw head with washer to hold the nut on the wrench
http://tinypic.com/kvxo5
to adjust tension simply loosen the screw and move the nut up (less tension) or down (more tension)
http://tinypic.com/kvxqg
i have tested this and think it is a great design, and hope you all can make similar objects, with it you have an extra hand to hold the lock, 2 handed pick, or other stuff too (like drinking a soda)