Donald Trump's wall: How tech guards the US-Mexico border
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Media captionWATCH: Nick Kwek toured the border dividing the US state of Arizona and Mexico's Sonora
“We gotta get outta here!” cries Agent Daniel Hernandez of US Border Patrol.
Moments earlier a hurled rock from over the fence whacked the tin roof next to us with an almighty thud. Its target: Agent Hernandez, my camerawoman and yours truly.
“You gotta limit your exposure when you're there by the International Fence, you know,” says Agent Hernandez, once we're safely back in his truck.
I do now.
We are in southern Arizona at the Nogales Border Crossing checkpoint.
While President Trump demands a wall costing several billions of dollars, and the Democrats suggest technology would be better suited to the job, we are being given a whistle-stop tour of some of the tech already in use within Arizona's Tucson Sector.
As we ride around, Agent Hernandez tells me ..