The United States, Canada and Mexico should establish a common security perimeter to guard against terrorism in North America, a tri-national independent task force said in a report released on Tuesday. The countries should police their borders together to help border trade, allow easier movement of citizens and to keep out potential security threats, the task force said at New York's Council on Foreign Relations. "If our two borders, the one between Canada and the United States and the U.S. and Mexico, became a frontline for security the impact that would have on normal relations and economic relations would be...