I have a cheap boot knife with a clip on the sheath, but it strikes me as even more likely to pull your sock down- or require you to tie your garter awfully tight.

There is a physics problem hidden here somewhere: Does a knife IN your sock exert more or less downward force than one clipped to the top of your sock?

I recognize that it could be hooked only to the garter, but then you have the additional problem of it flopping around. I suppose you could pass the garter through a couple of slits like some belt sheaths have, but it seems wrong to me, just wrong and troublesome...