As a bit of a side-note:
In Scouts I've found that a lot of boys lose their pocketnives when the knife falls out of the pocket while the boy is pulling other "stuff" out of their pockets. The other common way is simply by leaving it sitting on a table someplace, especially at summer camp.
These days I recommend to the Scouts that they get a piece of thin twine - preferably a bright color - that is a bit shorter than the distance from their belt to the ground. Tie a bowline knot on each end. Loop one end around their belt or a belt loop, and then loop the other end through the ring on their pocketknife. When not in use the twine is bunched up inside the pocket (preferably not hanging out of their pocket - for safety).
When using the knife this length of twine is plenty long enough to provide sufficient "reach". If the lanyard is short enough to not allow the knife to hit the ground, then if the knife falls out of the pocket they'll feel the tug on their belt (loop).
If the lanyard does catch on something, they'll only get hung-up from their belt or belt loop, so there is little real danger there - compared to a neck lanyard.
The best twine I've found for this is the bright synthetic string used for running the level lines in construction - I don't know the official name of this string though. Home Depot & Ace Hardware sells the stuff. They can use paracord, but it tends to be a bit of overkill and takes lots of room in their pocket. I've also seen the knots in paracord lanyards come untied in pockets - most likely from frequent jostling in their pockets, but this doesn't seem to happen with the level-line string. I've assumed that if the full weight of the boy is on the level-line string that the string would break (great for safety), but I don't KNOW that for a fact.