I have been pondering the idea of making a sheath for a while now. I haven't quite grasped the sword frog, and in real life, technically a sword frog is useless without a sheath anyway. This is the result of what happened when I messed around trying to make a sheath for my ninjato. It's not perfect; and I know, it's a back sheath, and you can't use back sheaths with full length swords. Nonetheless, here it is.
1) Duct tape
2) A thin foam sheet