"If you hire the right [smuggler] and are willing to accept the higher degree of physical risk, you can get through," Cornelius said. "But the older people are less tolerant of the kind of risks that young men are willing to take."
Sara Hernandez, a 49-year-old from Guadalajara, said the fear of getting hurt would keep her from trying again to cross the two fences that separate Tijuana from San Diego.
"The first fence I jumped. But I never dreamed there would be another one, and that it would be so, so tall," said Hernandez, who fell from the top and sprained her ankle. She eventually went home.
Few notice the border's strengthened defenses more than veteran crossers, who recall the easy passages of years past.
Armando Martinez, a 47-year-old farmworker from the state of Sinaloa in Mexico, crossed into San Diego in 1976. "I just walked across and caught the bus," he said.
In May, Martinez decided to avoid the heavily secured San Diego border and tried to slip through the desert east of Yuma, Ariz. Dizzy, dehydrated and hallucinating after three days, Martinez stumbled upon an emergency beacon and signaled the Border Patrol.
Martinez, a short, skinny man, said the days when he could endure such a long trek are over.
"I'm going to go home to pick crops," said Martinez, who was interviewed at a migrant safety office in the Mexican town of San Luis Rio Colorado. "I don't want to try crossing again."
Jorge Perez Diaz, 48, first came to the United States 25 years ago by walking along the beach from Tijuana. But when he tried crossing last year in the rugged hills east of San Diego, he was forced back by Border Patrol agents.
The disorientation and fatigue he experienced was enough to discourage Perez from making another attempt to reunite with his wife and three sons in San Jose. "I'm too old now to walk across these mountains," he said.
Fearing long, brutal treks through the desert, those not in peak physical shape often head to urban areas. That's where they confront America's most fortified borders.
At the San Diego-Tijuana border, the two fences -- the first 10 feet high and the second 15 -- line most of the frontier. Stadium lighting illuminates shadowy canyons. Motion sensors have been seeded across hills and beaches.
Most recently, video surveillance cameras have been erected, and National Guard troops have arrived.
