For many years, John Plaster (The Ultimate Sniper) notes, Israel’s northern border with Lebanon was under constant threat from infiltrating terrorists:
Finally, after many techniques and technologies were tried, an effective means was developed to detect and hunt down infiltrators. Along the southern side of the fence, Israeli military engineers scraped a simple dirt road, which a modified truck passes over each morning with a special brush-like drag to sweep and smooth the soil. The road is too wide for infiltrators to leap across, so inevitably they must step on it — leaving behind fresh tracks. Whenever such tracks are discovered, special tracker team immediately are flown in to hunt down the infiltrators. Except for one incident when an infiltrator flew across in a motorized hang glider — only to be shot down and killed — the barrier has proven quite effective.