I like the Repalas too. For a fixed blade knife, I've used those and other "kitchen" knives that have outlasted and out performed dedicated heavy "camping" knives. My trusty Chicago Cutlery boning knife is the same idea only slightly shorter and stiffer.
I make my sheaths from PVC and a heat gun. I'm sure you could sew ballistic nylon around them to make them softer, but they are pretty much indestructible as they are. They take about 30min. to make.

Kinda what I do:
https://www.youtube.com/watch?v=wXSQ8o5nKGc

Nice thing about this method of sheath making is that it's a form fit for the knife, and friction hold it in solidly. I do this also for my kitchen knives for picnics and car camping. Takes seconds since the belt loop isn't needed.
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