See also on this issue;
http://www.freerepublic.com/focus/f-news/2472521/posts
One reason DHS has been able to do this is an amendment that Sen. Kay Bailey Hutchison (R.-Texas) slipped into an omnibus appropriations bill that Congress passed on December 18, 2007. Hutchisons amendment put a loophole in the fence law that allowed the secretary of Homeland Security not to build the fence Congress had mandated the year before.