(AP) -- A marathon course runs 26.2 miles along an open road. Much tougher to secure than an arena with doors and walls.
Yet across the U.S. and around the world, from West Bend, Wis., and London this weekend, to Nashville, Tenn., next week and Copenhagen next month, organizers of road races are trying to figure out how to improve security after the Boston Marathon bombings.
Paris Marathon director Joel Laine, whose race was held earlier this month, put it this way Tuesday: "There will be a 'before' and 'after-Boston'" from now on.
Still, with thousands -- and sometimes hundreds of thousands -- of spectators and entrants scattered along the route, there are limits to how much can be done to protect everyone, marathon officials, experts and runners cautioned.
"This is a 26-mile foot race. With both sides of the street, that's 52 miles to secure," said Tom Derderian, coach of the Greater Boston Track Club and author of a book about the Boston Marathon. "How? You can't have everyone go through metal detectors."