The Portland Design Works Origami bike fender is great, but I found that it would slide from side to side while I locked and unlocked my bike. It's nothing major, but it was annoying to hear my bike wheel rubbing on it in the morning. Sugru should be able to fix this.
Step 1: Clean
First you have to clean the part of the fender that you want to apply Sugru to; I'm adding it to the top of the mounting bracket. I would have also roughed it up with some sandpaper, but it already was fairly scratched from being on my bike.
Step 2: Add Sugru
Add a few globs of Sugru and spread them out onto the mounting pad. It doesn't have to be too precise or pretty; no one will ever see it once its installed. I used more than I needed, but I had to finish off a 5g package and had run out of things to fix.
Step 3: Done
Clean the down tube of the bike and install the fender again. Let the Sugru dry before taking it out for a ride and the fender will never move again.