On a sprawling Brooks County ranch roughly 80 miles north of the Texas-Mexico border, sixth-generation South Texan Mike Vickers patrols his pastures on a four-wheeler.
"This is God's country," he said. "This is actually the old Brooks Estate. This belonged to Captain Brooks, the Texas Ranger that this county was named after."
With your closest neighbor nearly eight miles away, living this close to the border can present certain challenges. Since moving to the ranch in the mid-1970s, Vickers said he's seen plenty.
"We'd probably see a couple people a week that would come up to the front door – very courteous Mexican peasants looking for a job," Vickers recalled.
But that, he said, evolved into bigger groups of undocumented immigrants from countries other than Mexico.
"The disposition of the group started changing," Vickers said. "They became more demanding and aggressive and threatening."
By 2006, Vickers had enough.
He launched the Texas Border Volunteers, a group of nearly 300 men and women who gather monthly from places as far away as Florida, Nevada and Boston to conduct undercover operations along the border.
Just over a dozen members showed up when NBC 5 tagged along. Their mission is to hide on private ranches and report criminal trespassing.
The group we met ranged in age from their mid-30s to late 70s and included an attorney, a fire arms instructor, a retired airline pilot and several former members of the military.
Each person used a code name – like Ice, Cactus, Tall Boy and Pole Cat.
They must have a concealed carry permit, and if they see anything suspicious during their operation they call the U.S. Border Patrol.
"Some people think that we're doing a good thing. Some people think that we're just out here trying to be vigilantes," said Michael Torres.
Torres, 45, works for the Department of Defense in Corpus Christi and has been taking part in the group's undercover ops for three years.
"We've seen drugs, guns – it's all here," Torres said. "If you're scared, you shouldn't be doing it."
In the group's 11-year existence, they said only one member has ever drawn a gun and no shots were fired.
Unlike other groups with similar missions, the Texas Border Volunteers aren't allowed to carry long rifles and they're recognized by multiple law enforcement agencies across South Texas as an extra set of eyes and ears to help the Border Patrol stop undocumented immigrants.
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"It's like a cancer," Torres added. "We can't support it. We gotta cut it out, or at least slow it down."
"It can get very dangerous," said Chris Cabrera, spokesman for the National Border Patrol Council. "We have agents get attacked quite often."
Cabrera said the human smugglers are often connected to drug cartels and that the volunteers like the Texas Border Volunteers can be very helpful.
"They're not out there to do anybody harm or take the law into their own hands. They're just out there to observe and report it to authorities and let the authorities come in and do their job," said Cabrera.
We spent two nights monitoring a 35,000-acre ranch with Tom Kile, a 77-year-old North Texan who is retired from the U.S. Navy. Like others in the group, Kile is dressed in full camo. He's wearing boots that protect his legs from snake bites, and he's armed with a handgun, a two-way radio and two night-vision cameras.
"I think of us as being like a neighborhood watch," Kile said. "I do it because I think we need to enforce the laws."
Once the sun went down, we sat with Kile under a mesquite tree and waited for more than five hours. He drank coffee to stay awake and sprayed himself down with bug repellent to keep the pesky mosquitoes away.
"There has been one case of Zika reported not far from here," he said.
We never saw any activity, aside from deer, hogs and wild turkey. But in a previous border op, less than one mile from our location, another member shot video of a group of 60-plus people hiding under the brush.
That group managed to bypass multiple Border Patrol checkpoints, but they didn't elude the Texas Border Volunteers.
"Since our inception about 11 years ago, we've reported a little over 2,000 people and the Border Patrol has apprehended a little over 1,700 of those," Kile boasted.
The Texas Border Volunteers have dozens of pictures to prove it.
Border Patrol stats show the Rio Grande Valley, which includes Brooks County and McAllen, is one of the busiest border sectors in the United States.
In 2014, Border Patrol agents in that sector caught more than 250,000 people trying to sneak into the U.S. illegally.
That's more people than the populations of Frisco plus all of Rockwall County combined.
However, in recent months, the numbers appear to be slowing.
"In January, McAllen had a little under 10,000 apprehensions. In February we cut that in half, to just about 4,000, and in March we were under 2,000," said Cabrera.
He credits President Donald Trump's administration.
"One thing we haven't had in the past eight to 10 years is a political will to enforce our borders, and right now it seems like we have that political will," Cabrera said.
"These are big, big ranches with a lot of cover," said Vickers.
It's also his home, a place worth protecting.
"I've got some friends that have been threatened by the cartels and they've left, but a lot of us are staying. We're not leaving and we're going to continue this fight until our border is secure," Vickers said. "We're optimistic; we think someday maybe it will be secure."