Federal officials within weeks plan to start construction on a new "virtual fence" along the U.S.-Mexico border. Plans are expected to be formally announced tomorrow. Supporters say the system could almost completely cover the nearly 2,000-mile frontier within five years. The first permanent towers with sensors, cameras and communications gear to detect drug smugglers and illegal immigrants will be built along 53 miles of Arizona. Customs official Mark Borkowski says more towers will follow on the remaining 320 miles of Arizona's southern border. Borkowski says virtual fencing then will go up in New Mexico, followed by California and most of...