Bit of a thread bump here, as I finally got around to making a bark sheath, and I thought I would post the pictures here, rather than start a new thread.
So here is my attempt at a sheath for my home made small woodcarving knife.
Birch bark sheath by
Alan Muddypaws, on Flickr
Birch bark sheath 2 by
Alan Muddypaws, on Flickr
A bit rough and ready, and no belt loop (this broke during the making, as the bark was quite thin), but I only need to protect the knife in my carving tool pouch. This will replace a cardboard and duct tape blade cover.
So thank you Neil for the video and the inspiration!