Destitute and determined to sneak into the United States, Alvaro Garcia arrived at a Tijuana shelter after a 60-hour bus trip from southern Mexico to rest and inquire about the most porous spots along the border.

Planning to cross by himself, he learned from other migrants about Nido de las Aguilas, a shantytown on the outskirts of Tijuana where rugged hills interrupt a metal fence dividing the United States from Mexico.

"I'm willing to do anything to get to the other side," Garcia said. "I just needed to know where to do it."

Migrants with money hire smugglers to lead them across the border, especially since 1994 when the United States increased its border patrols and began erecting fences. But some, like Garcia, lack the cash to pay fees of up to $2,500 and must rely on their own wits to get across.

The trip will likely become even more difficult next month, when the first of 6,000 National Guard troops promised by President Bush begin assisting Border Patrol agents. The construction of 370 miles of triple-layered fencing is a key part of the immigration bills being considered by Congress.

The extra security could make sneaking into the United States riskier, especially for those trying to go it alone.

CountryWatch: Mexico

For lone migrants approaching the border, the first stop is usually a shelter where they can find partners for their journey. They learn from other crossers which hills and canyons to take, the best time of day to cross, the places to avoid and where they might hide from the U.S. Border Patrol.

But hazards abound. Migrants crossing alone in remote areas often fall prey to bandits who hide in remote canyons, in the barren desert and along the Rio Grande riverbanks. Unfamiliar with the rough terrain, they must survive the desert's harsh heat during the day and biting cold at night.

The bodies of 2,881 migrants have been recovered by the U.S. Border Patrol since 1998, when the agency began keeping record, and many more remain missing.

No official figures exist on how many of these were trying to sneak in on their own. But border experts say crossing without a smuggler raises the risk of dehydration or hypothermia after getting lost in the desert, or of drowning in the Rio Grande.

"Those who cross without knowing the area are more likely to drown because the river may seem calm. But it has proved otherwise many times," said Arturo Solis, president of the Center for Border Studies and Promotion of Human Rights in the border city of Reynosa, across from McAllen, Texas.

More than 1,200 bodies have been found floating in the Rio Grande near the northern state of Tamaulipas' border with Texas since 1994, Solis said. About half were never identified.

Still, the risks are rarely a deterrent for migrants desperate to improve their economic situation and help their families.

Garcia, a 30-year-old construction worker who traveled 2,300 miles from southern Tabasco state to Tijuana, just across the border from San Diego, said the $150 he made per week was hardly enough to support his wife and two children. He decided to head north after racking up a hospital debt of $3,500.

"I was told I would have to bring plenty of water, that I'm going to walk a lot and that the journey is dangerous, but I have to at least try," he said.

Experts say migrants who try to sneak into the United States without a smuggler also are more likely to be caught by the U.S. Border Patrol. But then they're simply dropped off on the Mexican side where they quickly try again and again, a process that helps them eventually master the ropes of border crossing.

"They are caught and released, caught and released, and that's how they learn what they need to do to reach their destinies," said Jorge Bustamante, a senior researcher and former president of El Colegio de la Frontera Norte in Tijuana.

Jose Olivares, a farmer from the northern state of Zacatecas, crossed successfully on his own near Yuma, Ariz. Once on the U.S. side, he jumped on a freight train heading to Pico Rivera, in southeast Los Angeles County, where he soon found work.

Olivares painted houses for $7 an hour until he was detained by police for drinking on the street and deported to Mexico.

Waiting to have a warm meal at a migrant shelter, Olivares said he planned to travel to the Yuma border and cross again.

"I don't have any money to pay for a smuggler, and I've already crossed on my own," he said. "I already know the way."