I do recall seeing some talk of Boeing using implanted metal fibres both for lightning and electrical conductivity as well as detecting fuselage damage. Any break or distortion in the grid would be detectable by a system that they have cooked up under various patents.
Obviously all top secret and patented but along the lines of an electrical pulse being sent out and any deviation from the norm provides an 'echo' pinpointing the area to be looked at. They can then do something akin to those whizzy Autoglass type repairs where a resin is forced into any crack and it then sets harder than the original.
