Walls alone won't seal US borders (Image: KPA/Zuma/Rex Features)From New Scientist:
A MIGRANT makes a furtive dash across an unwalled rural section of a national border, only to be confronted by a tracked robot that looks like a tiny combat tank - with a gimballed camera for an eye. As he passes the bug-eyed droid, it follows him and a border guard's voice booms from its loudspeaker. He has illegally entered the country, he is warned, and if he does not turn back he will be filmed and followed by the robot, or by an airborne drone, until guards apprehend him.
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My Comment: It will be expensive .... but it will probably secure the borders.