If you know of an old fridge that is being thrown away then swipe the magnetic strips from the door seals. Superglue some of these strip magnets to a suitable size piece of leather, and hey presto! instant sheath that wraps round and sticks in place by magnetism.
My drawknife has one of these sheaths, and I was thinking of adapting the idea and making a longer one to cover a bow saw blade.
Hope this helps, but I'm sure other more traditional leather workers may suggest other ideas.