A fence already marks the U.S. border with Mexico but in some places, it's no more than a strand of wire or metal rail.

Where a real barrier exists, it works. Illegal immigrants (search) are forced to travel long distances to get around miles of tall steel and razor wire.

Click in the video box to the right for a complete report by FOX News' William LaJeunesse.

Now, a group of border activists are pushing for a new, bigger fence — more like a Berlin Wall — from the Gulf of Mexico to the Pacific Ocean.

"If we don't stop the illegal immigration problem at the border, the problem will grow in far more dangerous ways ... because illegal immigration from Mexico provides easy cover for terrorists," says one national television ad sponsored by Weneedafence.com, a project of Let Freedom Ring, Inc.

The TV spot focuses not on the politically charged issue of illegal Hispanic immigration but border crossers who may be a security threat, especially those caught who originated from suspected sponsors of state terrorism (search).

"What are people from Yemen and Syria and Iran doing in Mexico trying to enter the U.S. illegally? This is an issue that requires a wall," said Colin Hanna of Weneedafence.com. "We are absolutely not anti-Hispanic, we do not think the fence should be perceived as anti-Hispanic, or anti-Mexican, we are not anti-immigrant, we are pro-immigration, but we are pro- legal immigration."

Hanna's group hopes to persuade Congress to take on the $8 billion project but aside from the cost, Hispanic activists claim that good neighbors build bridges, not fences, and that a fence will stigmatize people fighting for their shot at the American dream.

"I think what we're doing is criminalizing work and criminalizing the need of families to be together," said Angela Sanbrano of the Central American Resource Center, an open-borders interest group.

Years ago, the idea of a great wall on the southern border would have been dead on arrival in Congress, but times have changed. Polls now show that more than 80 percent of Americans like the idea, and it has bipartisan support. One House bill has bipartisan support but is nowhere near ready for passage by the entire Congress.

Many Democrats favor the concept because the downward pressure on wages from illegal immigrants is hurting organized labor (search). Republicans, meanwhile, also like the wall for national security reasons.