To add to what BDA has said, if you're missing ones at the rear arches, I'd clean out the sill and check the seat belt mounting plates which are just ahead of the fuel tanks. Mine had rusted away, one of those "out of sight, out of mind" things about these cars.
On the wheel arch shields, I made mine from 1mm Aluminium and used hefty stainless self tappers to hold them in place. A bit of tape over the screw head to keep off the dirt and it's very easy to remove them should you ever need to.
Brian