I used to have this problem loads with the Associated CVA's back when I was running their cars. Back then the main culprit was always the back propshaft in the B44 - the pin would come out and cut a nice groove in your lipo's
What I do now is put a dot of threadlock into the groove in the axle where the retaining ring sits, make sure to put the dot at 90 degrees to the CVA pin so you don't threadlock your driveshaft solid!
The threadlock is enough to stop the ring spinning but dead easy to release when you want to take everything apart.