magnets are available
72 inches wide for $179 on amazon
but they really only work well at slow speeds around parking areas etc
they would work well around nail spills, accidental or on purpose
since the majority of flat tires are on the back tires, from the front ones disturbing the nails on the road
i have seen magnets hung like mudflaps in front of the back tires
he said he removed them after a while because
the strong earth magnets fell apart in the weather - unlike a magnetized bar
he thought the nails were flying to fast to stick - they just bounced off
mud and snow build up were trying to rip them off