"Though strings to shape the parabola followed by chicken wire and ferro cement covered in foil would probably make a more durable one."
Durable, maybe, but not the most efficient. Hundreds of razor blades stacked next to each other will funnel and absorb much more solar energy. Anything that looks "shiny" is losing too much energy in the direction of your eyeball.
Ahhh.
I'm sure you're much more up on the science of such things than I am. Been a while since I've read much on it, anyway.