use to carry a large knife in that position.  i used velcro strips, normally used for securing computer or other electrical wires.  the kydex sheath had attachment holes that accommodated them.  after several years i relocated it to inside the pack.  i felt i had no need for immediate use - useless against bears, lions are faster, and outside carry might antagonize knuckleheads.  and i've read that in a knife fight, someone dies.
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“Everyone should have a horse.  It is a great way to store meat without refrigeration.  Just don’t ever get on one.”
 - ponder's dad