From this:

Appropriators dropped a requirement in the 2010 Homeland Security spending bill to rush the construction of a fence at the Mexican border, disappointing conservatives who pushed the project as a way to slow illegal immigration.

The conference report for the $42.8 billion appropriations bill left out language in the Senate's version that required the installation of 700 miles of the border fence by the end of next year. The fence requirement was inserted in July as an amendment sponsored by Sen. Jim DeMint (R-S.C.). It was adopted with the support of most GOP senators and 21 Democrats.

But the conference report went with the House's position, which didn't include any requirements on the fence's construction.

To be frank, a fence would not be necessary if politicians realized that supporting illegal immigration would harm their careers. The way to help that come about is by asking them tough questions about illegal immigration on video; see the two-and-a-half year old plan in question authority, and ask your leaders why they haven't been promoting that plan but instead have been at the most encouraging you to engage in ineffective activities such as acting out at townhalls.