Muon tomography uses naturally occurring cosmic ray muons to image up to a kilometer of intervening material on the surface of the earth.  It has been utilized to "x-ray" a variety of structures from volcanoes to nuclear reactors.  A research agreement between Occidental College and a mineral exploration company has allowed the construction of a high-resolution TPC for use in a borehole.  A discussion of the detector and early results will be presented.  A recent publication on the feasibility of using borehole detectors to discover illegal border tunnels will be described.  Finally a speculative idea for the future will be discussed.