I am surprised this is not a well known system. I suggest more advertising around the United States and other regions in need of tunneling detection. I will be using this information on a paper, you SureWave will be credited. Thank you for finding solutions, UK!
Cant they dig pass the tunnel detection system by digging further, or shit even having multiple, if not hundreds of potential exit points? Whats to stop them creating a machine that vibrates the ground like a jack hammer? Maybe im over estimating what people would pay to an engineer to have this defeated, who knows.