It is terrible to find yourself beset by Heliopan and B+W filters that keep coming loose but don’t have slotted retaining rings so you can get a grip. At best you have rattling glass. At worst, a ring screwed in from the back can let the glass hit the front surface of some lenses or jam your Hexar AF’s focusing system.
Here is a quick trick: take a popped (and clean) “punch ball” balloon (the type children have with the rubber band attached to the top), lay it it over the retaining ring you want to turn, and push your fingers to the edges (so you are pressing laterally on the retaining ring through the balloon.
Now rotate the retaining ring (with your fingers) clockwise (locking ring facing up) – or turn the filter mount counter-clockwise (the lens glass and retaining ring should always rotate in the same direction). After you get a feel for it, the ring will screw in and secure the glass.
For extra never-come-unscrewed-again-ness, add a tiny drop or two of Loctite® Purple to the threads of the retaining ring (you have to take it all the way out before you do this). Make sure that you get all the thread locker off the glass before it dries and be sure that ring is screwed down tightly.
By the way, this trick can also work with retaining rings that are slotted, as well as lens beauty rings. Be aware, however, that for high-value optics, you want to be very, very careful in touching the glass with rubber that could be contaminated with grit.