PENITAS, Texas — The border fence behind Manuel Zamora’s home suggests strength and protection, its steel poles perfectly aligned just beyond the winding Rio Grande. But every night, the crossers come. After dark and at sunup, too, dozens of immigrants scale the wall or walk around it, their arrival announced by the angry yelps of backyard dogs.
“Look,’’ Zamora said early one recent morning, ‘‘here they come now.’’ He pointed toward his neighbor’s yard, where a young man in a dark sweatshirt and white sneakers sprinted toward the road, his breath visible in the winter dawn. Three others followed, rushing into a white sedan that arrived at the exact moment their feet hit the pavement.
‘‘I don’t know how the government can stop it,’’ Zamora said, watching the car drive away. ‘‘It’s impossible to stop the traffic. You definitely can’t stop it with laws or walls.’’
The challenge has tied Congress in knots for decades, and as lawmakers in Washington pursue a sweeping overhaul of immigration, the country is once again debating what to do about border security.
By every indicator, illegal migration into the United States has fallen tremendously — in part because of stricter immigration enforcement — and has held steady at lower levels for several years.
But visits to more than a half-dozen border locations over the past two years show that the levels of control vary significantly along the line.
Many areas that used to be popular crossing points have experienced undeniable improvements.Other sections of the border have seen less progress.
The government-wide spending cuts that went into effect Friday could make things worse.
It is increasingly clear to those who live along the boundary with Mexico — or who try to protect it — that there is no such thing as a completely secure border, just as there are no cities without crime.
Even in areas with towering walls and drones or helicopters overhead, border security can be breached.
‘‘The US border with Mexico is better controlled than at any time in our history,’’ said Robert C. Bonner, who served under President George W. Bush as the commissioner of the US Customs and Border Protection. But, he said, there is a lack of understanding among policymakers and the public about the challenge.
‘‘The terrain can be quite different depending on what part of the border you are talking about, and there are different ways, different tactics really, that need to be brought into play,’’ he said. ‘‘And this requires almost mile-by-mile analysis.’’
Suly Ochoa, 56, a home health care aide whose house sits along the border wall in Granjeno, Texas, says that what she wants from the border policy is simple: ‘‘It needs to be smarter.’’
Like many of her neighbors in this town of 303 that was founded on Spanish land grants in 1767, she and her family have seen immigrants crossing through the area’s mesquite trees and tall grass for decades.
They have often helped the most desperate, calling ambulances for children or pregnant women. But residents have become increasingly concerned about security as Mexican drug gangs seized the business of moving people and narcotics.
Crime in the larger area of McAllen, Texas, while low, now occasionally includes what appear to be targeted killings.
Ochoa said she and many others in Granjeno had hoped the $20 million border wall — a 1.7 mile stretch of concrete and dirt, rising 18 feet — would help them feel safer. Now, a few years after completion, it looks to her more like a waste. ‘‘It’s not working at all,’’ she said, standing near the wall. ‘‘To me, it’s money down the drain.’’
Part of the problem is that the fences and walls cover a limited area in the Rio Grande Valley sector — just under 54 miles staking out a relatively straight boundary near the 316 curving miles of river border. And even within the fenced area, because of the riverfront farms and parks, there are several gated openings.
Ochoa says she sees drug loads at least once a week — usually large pickup trucks with bales of marijuana in the back barely covered with a tarpaulin. Immigrant crossings occur almost every night, usually in groups of 10 to 20 people.
Yet Border Patrol officials say they are doing more than ever. In the 1990s agents here recall not having a budget to keep their gas tanks full. Now staffing levels in the sector have more than tripled, to about 2,500 agents.
Additional intelligence comes from drones and helicopters, along with cameras set up by the state to track wildlife.