“Look out!” Kane heard the shout and turned around to see who was shouting. A second later, a mountain biker whooshed past him. The biker turned his head and shouted “Bikes only, asshole!” and disappeared from view. Kane was walking on a mountain bike trail. He had already seen a sign saying Bikers Only, but he had figured that the trail in the woods was wide enough for him and for the bikers.

This was public land. Who were bikers to hog this trail for themselves, he thought. Where was he supposed to take his nature walks—through the spider webs and the underbrush? And who did that biker think he was, to call Kane a name? The more he thought, the angrier he got. He’d fix them.

The next Saturday, he visited the trail again, but this time with a shovel. It was an old GI shovel that he still had from his Army days. It was small but efficient. He found a slight curve in the trail and, just after sunrise, he started digging. He dug a ditch all the way across the bike trail. The ditch was four inches deep and twelve inches wide. He would have liked to hang around and watch the action, but there was no place to conceal himself. Maybe later he could set up one of those spy cameras people use for home security, he thought as he walked back to his car. Then he could upload the really good crashes to the Internet.

An hour later, a 15-year-old girl hit the ditch. She flew through the air and landed among some small trees. Because she was wearing a helmet, knee pads, and elbow pads, all she suffered were bruises, scratches, and a sprained wrist. Her $700 bike was moderately damaged. She used her cell phone to call her dad. Despite her soreness, she stood guard on the trail to warn others.

Police investigated the scene of the "accident." An officer said if they caught who dug the ditch, the culprit would be charged with felony vandalism, which might result in a year in prison.