I carry a knjfe, either in my sock top or boot top quite often.
Here is my 2 cents worth.

1. the knife blade should be under 4"
2. the shearth should extend @ least 1/3 the way up the handle ( as mentioned, easier to resheath )
3. the end of the sheath should br "rounded (esp. if worn in the sock.) (better "profile & less sogk wear )
4. BACK the sheath wth Lambs wool. (comfort & it helps keep it in place )
Here is a pic of the 2 kives I carry most often & the type of sheath that I recomend.


Puffer