Mexicans say it will take more than three layers of fence and 6,000 National Guard troops to keep them out of the United States.

Hundreds of protesters rally on the National Mall in Washington, DC, to press Congress for immigration reform. Senators took a swipe at illegal immigration, ordering construction of a fence along hundreds of kilometers of the US-Mexico border, even as Hispanic activists pressed for immediate immigration reform.[AFP]

As U.S. President George W. Bush on Thursday visited the stretch of Arizona desert that serves as a cactus-studded freeway for thousands of undocumented migrants, those preparing to make the perilous trip said they will find a way around almost any obstacle.

Increased security could also lead smugglers to raise their fees, driving immigrants deeper into debt and making them even more desperate to make it north.

While a tired, bedraggled column of deportees filed across a Nogales border bridge _ just as Bush was giving a speech on border security west of here _ some migrants used cell phones to contact migrant smugglers for their next attempt.

"Of course we'll cross again. We're just waiting for them to come and pick us up," said Javier Torres, 22, of the northwestern Mexican city of Culiacan. Just 100 yards (90 meters) away, vans like those used by smugglers waited at an underpass to pick up groups of deportees.

Martin Doriane, who for the last four years has surveyed returning migrants for the Colegio de la Frontera Norte, greeted the deportees on the Mexican side.

Doraine says at least 95 percent of migrants deported say they will try to cross again, partly because they've pawned everything they own in Mexico to pay for increasingly expensive and sophisticated smuggling efforts needed to overcome tightened border security.

"They say, 'I had a roof and a frying pan in Mexico, but I sold both to come north, and went into debt, so what do I have to return to?"' Doraine said.

One of the deportees, Maria del Carmen Valadez, brought her 12-year-old son, Julio Cesar Castaneda, on the dangerous two-day trek through the desert. The boy hungrily ate a taco Doriane had given to him as his mother acknowledged that "it is a risk" to bring her child on the trip.

"I did it to give him a different life," said Valadez, of Fresnillo, in northern Mexico. She said she'll probably try to cross again, because in her hometown, "there's nothing but poverty."

That sense of desperation _ and determination _ is everywhere.

On Monday, a detained woman told agents she had left her 3-year-old son dead in the desert.

Jesus Santana, a Tijuana truck driver who was recently deported, said there are no obstacles the U.S. could put up that will stop migrants.

"We'll go under it, we'll go over it, we'll go through the air, the sea or the earth, but they're never going to stop us from crossing," Santana said.

Mexico's government says the expansion of the barrier and deployment of the National Guard aren't the way to solve problems of border security and illegal migration.

"Building walls, constructing barriers on the border does not offer an efficient solution in a relationship of friends, neighbors and partners," Fox said Thursday in Tijuana. "We will go on defending the rights of our countrymen without rest or respite. With passion we will demand the full respect of their human rights."

Foreign Secretary Luis Ernesto Derbez said that Fox has sent a diplomatic letter to the U.S. State Department outlining his concern.

The proposed 595 kilometers (370 miles) of triple-layer fencing, approved by the Senate on Wednesday, as well as Bush's plan to send National Guard troops to play supporting roles in border enforcement, have raised tempers and tensions here.

"Somebody is going to start shooting, and then there will be problems between the two countries," Santana predicted.

The Senate measure, which has yet to be approved, includes provisions that would give some undocumented immigrants a path toward citizenship and allow more people to work temporarily in the United States.

But Santana said Americans are mistaken if they think they can stop illegal immigration.

"There will always be more people wanting to come," he said. "It will always be like this."