Question

If you put something like cardboard between the magnet and the nail, the magnet will still hold the nail in place even if the magnet doesn't touch the nail.

Answer 1

Magnetic-field lines pass through cardboard, air, and certain other materials, depending on whether they're permeable or nonpermeable. Test different materials to see which gather magnetic lines of force and act as magnetic shields, and which allow magnetic lines of force to pass through them.