There's steel toed shoes. Why not steel soled?
Step 1: Find Some Metal
Find some meta to make an insole out of. It should be thick enough that a nail wont go through it if you step on one but not super thick. As long it still has a bit of flex to it, where you could bend it with your body weight by stepping on it, it shouldnt impede your walking.
I used the cover pane of an old gas furnace. I would say its about twice as thick as a desktop computer case. Maybe a bit more.
Step 2: Trace and Cut.
Trace the appropriate sized insoles onto your metal. Dont try to just trace your foot if you have wide feet like me because the metal insoles have to be the size as the bottom of your shoe. They can spill over the sides like your feet or they will stretch out the uppers and mess up the fit of your shoes.
I cut the soles out with a grinder. It's like cutting out something with scissors. Even though it only cuts in a straight line, you can still cut out curves by making multiple straight cuts at different angles. See the picture. Even though you're cutting curved lines, only cut straight with the grinder. You can trace out a curve with the grinder by using very little to no pressure, sort of drawing/etching, but do not flex the cuttingwheel or you risk shattering it. This is just basic grinder safety. Dont bear down on a cut you are making unless it is a straight line running in the same direction as the wheel is turning.
Step 3: Thats It.
Put the metal insoles in your shoes and go step on some nails. Or dont and just be more safe in the event that you would step on a nail. I stepped on a plastic box of miscellanous nails the other day barefoot while carrying a mountain bike, my foot breaking through the plastic case, resulting in three nails about a half inch into my foot. What are the odds? Three for one? It happens though. Not the end of the world but not the beginning of it either.