KenK--

I don't generally like clip-on sheaths or holsters for the reasons Eaglescout and you both described, though some clips are better than others. Anything that fits the belt well, and curls under it (only have seen this in a "plastic" clip--never metal) is fairly reliable. The paradigm of this type is used by Lou Alessi on his Talon Nyclip IWB (inside-waistband) holsters. I have also used a couple of paddle-style holsters with both confidence & success.

However, clip-on knives are another matter entirely. You do realize that the knife is clipped inside the pocket or waistband, and that only the clip itself is on the outside--not the entire knife? For extra security, clip the knife inside the waistband of your pants, but beneath the belt. That way, the belt both hides the clip, & helps hold it in even tighter.

Carried in the proper manner, they're safe & secure. I've even slept with a knife clipped into the waistband of my shorts, or in my pocket.

The clips are not absolutely failsafe, though. Some care & attention must be exercised. I've had a Spyderco Delica plucked from my left-hand front pocket a couple of times by my seatbelt, and an older, plastic-clipped Delica once spent the night on the floor of a conference room where the arm of the chair had caused it to slip unnoticed from my pocket. (I retrieved it straightaway the next morning, thankfully.)

David