Give this a try...
There are a couple pretty simple things you can try:
- Try stretching out th detente springs a bit with your fingers or some needle nose pliers. This will energize/preload the ball bearings a bit more and provide more load on the underside of your u-turn cap to (hopefully) prevent it from winding down on you.
-Alternatively, buy another set and double up on the balls and springs. Fill all the holes with a new spring and ball.
Oh, you could also remove the grease from the spring and helix inside your fork. More friction will probably make it harder to turn, both intentionally and unintentionally.
Hope this helps
-Cheerio-