That's a neat site, Tim.

I was thinking about how to make a target last night. Since the axe edge will most always hit vertically, why not arrange a few beams or thick planks (4-5 feet long) side by side vertically? Kind of like a giant laminated cutting board.

Glue and clamp them together then secure some cauls to the back or a backing of 3/4" plywood. A couple of legs (attached to the back w/ hinges?) and you're ready to take aim.

It would be heavy, but should hold together as the axe will penetrate parallel w/ the grain.