Remember the Secure Fence Act of 2006. If you read the text
it is pretty specific about having the DHS work towards at least two layers of fencing all the way from 15 miles before Laredo to the Brownsville port of entry.
However, as one travels the border in that area, not only is the area incomplete but one really doesn’t see border fencing.
What happened? An important clue comes from the following year as this article explains:
This was modified the following year by an amendment added to the 2007 appropriations bill. The sponsor was TX Senator Kay Bailey Hutchison and co-sponsored by all the other senators of states along the Mexico border (TX, NM, AZ, CA), five Republicans and three Democrats in total.
The amendment gave DHS much more leeway on how the border might be secured and also said DHS needed to consult with local communities along the border.
A good example of how if you don’t have local support, something that looks attractive on TV may not really happen the way you expect.