Republican presidential candidates are debating the merits of a fence along every inch of the United States' border with Mexico, with Texas Gov. Rick Perry saying it isn't the best way to fight illegal immigration.

Rep. Michele Bachmann of Minnesota said Tuesday she would build a double fence along the southern border. She says the country spends $113 billion each year to provide benefits to illegal immigrants.

Rep. Ron Paul of Texas says the fence is not the answer, agreeing with Perry. Former Massachusetts Gov. Mitt Romney says a fence would help but the way to cut illegal immigration is to end benefits for them. That was a jab at Perry, who signed a law that provides in-state tuition for illegal immigrants.