Seriously, why not use satellites with infrared cameras? Sure, they don`t work in cloudy weather, but how much cloudy weather do you see on the Arizona-Mexico border?
A reader writes:
I was looking at a globe today as I dusted. If a satellite orbits over 32 to 35 degrees latitude, it flies over the Mexican border and also Iran, Iraq, Israel, Pakistan, and Afghanistan. . . Do you suppose we have any satellites flying there?