"In 2006, the Secure Fence Act was signed into law, requiring the Department of Homeland Security to build upward of 700 miles of double layered fencing along the U. S-Mexico border. While the Obama administration is quick to state that the targets have been met, only a small fraction - in fact, less than 40 miles - of the newly implemented infrastructure is double-layered."
Source : Jim Loehr, Dr. James E. Loehr, Tony Schwartz (2005). “The Power of Full Engagement: Managing Energy, Not Time, Is the Key to High Performance and Personal Renewal”, p.5, Simon and Schuster