How to prevent Distributer from slipping??

Went riding today and the timing slipped a bit, the jeep ran fine all day, but when i shut it down it deisels and it is a little harder to start back up. I know i had it timed correctly adn ran it fine about a month ago. i know it slipped, just havent put a light to it. So my question is, what can i do to keep the dizzy from slipping? At first i had a differnt clamp to hold it down, i got the correct hold down convex washer abotu a year ago, and it just doesnt seem to hold. I was thinknig bout pulling the distributer and notching it and making a hold down that will keep on the notch. What do you guys suggest? I am also not sure how much torque an aluminum cover can handle for tightening it down. i have it good and tight, but i didnt go super strength to get it tight. What have you guys done to cure the moving distributer??

 

Seems to me if the hold down tab isn't bent, it should hold...... (shrug)

 

The hold tab, is actually a convex washer. it should hold, but i dont think it does. i am not sure if i "marked" the housing to see if it moved, if not i will mark it and drive it around and see what goes on