I have the Buck 119. The total length of the knife is 10.5 inches and you can add on a bit more for the sheath. That is lot of knife to be hanging off the shoulder strap of a backpack. That said, when I carry the Buck, it goes in the top external pocket of the pack and although it is not fully and readily accessible, it is still not that difficult to get to if needed.

Hikermor mentioned zip ties. However I am not sure they would work if the newer sheaths are like my old sheath which is fairly thick, stiff and very slick. The zip ties to hold the sheath 100% in place upside down would need to fairly tight to not squish the sheath to the point that the knife is difficult to remove/insert back into the sheath.

With the sheath and most backpack straps being black,you may want to utilize a couple or 3 narrow strips of black duct or gaffers tape in order to keep the neat appearance you are looking for.


Edit: Curiosity got the best of me. I tried the zip ties (only have white.) As I suspected, I would really have to crank the ties up tight in order to keep the sheath from eventually working it's way lose. Although that could be mitigated by adding another tie around the sheath right under where the handle strap is.

Still I would rather keep the knife in the backpack pocket as that knife is too big to be carried in this manner for me.