I like to carry either a Swiss Army knife or Leatherman Squirt in my pocket because I'm always using them for little tasks. So, to keep them from falling out when I sit down, I add one of those ubiquitous accessory carabiners to the key ring and hook it inside the edge of my pocket.

A secondary advantage is that it carries vertically in my pocket, which keeps it from turning sideways and pressing into my leg or potentially wearing a hole in the lining --another way to lose your knife.

When I want to use the knife, I just rotate it out over the top hooked portion and completely off of the carabiner. Or in the case of the Squirt, I leave the carabiner on and use that as additional handle space.