Which structure currently operates as a "virtual fence:"  Boarder Wall or Mexico-United States Barrier?
Mexico–United States barrier The Mexico–United States barrier is a series of walls and fences along the Mexico–United States border aimed at preventing illegal crossings from Mexico into the United States. The barrier is not one continuous structure, but a grouping of relatively short physical walls, secured in between with a "virtual fence" which includes a system of sensors and cameras monitored by the United States Border Patrol. As of January 2009, U.S. Customs and Border Protection reported that it had more than 580 mi of barriers in place. The total length of the continental border is 1,989 mi .
Fort Covington–Dundee Border Crossing Fort Covington-Dundee is a border crossing connecting Sainte-Agnès-de-Dundee, Quebec, in Canada to Fort Covington, New York, on the Canada–United States border. It can be reached by Quebec Route 132 on the Canadian side and by Dundee Road on the American side. The crossing is notable because the boundary line crosses through the now-defunct Taillon's International Hotel, where it was possible to order a drink in Canada and play pool in the United States. The hotel was built in 1820, prior to the Webster–Ashburton Treaty of 1842, which redefined this section of the international border.