No need. The smugglers (or, as I suspect, their bribees in the Mexican Army) have been known to actually go out with metal detectors and radio direction finders to hunt the sensors down.
"....Next they'll be telling Mexico where the Border Patrol buries its seismic sensors....."
or maybe just sell them 'seismic sensor detectors' !
No need. The smugglers (or, as I suspect, their bribees in the Mexican Army) have been known to actually go out with metal detectors and radio direction finders to hunt the sensors down.