RAFAH, Gaza Strip - In houses along the steel wall separating Gaza and Egypt, the lights are flickering — a sign that smugglers are digging tunnels below, their powerful drills weakening the flow of electricity. Tunneling is the fastest-growing business in this impoverished border town, and one of the biggest obstacles to any lasting Israeli-Palestinian truce. Since Israel pulled out of the Gaza Strip a year ago, the number of tunnels for smuggling weapons, drugs and other contraband has more than doubled, evolving into an underground maze clawed out of Gaza's soft soil. The largely unhindered weapons influx also heightens...