An impenetrable electric barrier will prevent surreptitious crossing of a border or perimeter of an installation. It consists of rows of vertical electrodes installed underground or above ground. It has two modes of operation. In an RF heating mode a generator powers electric fields to heat the ground in a pattern around the fence. A temperature may be reached which makes human occupation of tunnels untenable. Humans may also be subjected to RF radiation effects, especially if the frequency is tuned to a resonant frequency of tunnel cavities. Detection of a resonant frequency by suitable instrumentation may also indicate the presence of tunnels. In another mode occupants of a tunnel may be subjected to shock from an electric pulse, without heating, depending on small amounts of moisture to transmit the pulse through soil to the tunnel.
