Last summer at Denton Hill I met a guy with a cool behind the back cross draw knife sheath. I even took a tracing of it...but I was never comfortable with the security in leather. When I'm drawing the knife sight unseen, I want to make sure it is fitting very tight, wouldn't fall out especially if you sit down, and is easy to put the knife back in.
Backing up a bit...
My knives are not the fancy type that you would have a hard time taking them off the display shelf. They are meant to be used even abused. So Kydex has become a favorite way to keep them secure in the field for me.
The cool thing about Kydex and Chicago screws is that if you drill the same spacing on each side of the sheath...you can switch the belt loop to either side with the blade edge up or down. Now you have an off side cross carry or a behind the back cross carry in either RH or LH.
Right hand behind the back carry, my right hand thump pushes against the top opening of the Kydex sheath to start the knife out and my left hand holds onto the sheath...quick, easy, safe, and out of the way to draw my knife. Also easy to put the knife back in the sheath as it can only go in one way plus you won't cut through the Kydex like what could happen with leather...tippit