Described is a boundary proximity determining system for wirelessly defining a boundary having a programmable shape and for indicating the occurrence of a rover unit traversing the boundary. The boundary proximity determining system includes a base station unit that generates a plurality of magnetic fields. The boundary proximity determining system also includes a rover unit that is responsive to the generated magnetic fields such that the rover unit defines the boundary in terms of the intensities and polarities of the magnetic fields. The rover unit determines whether the rover unit is within or outside the boundary by determining the current location of the rover unit in terms of the intensities and polarities of the magnetic fields and comparing the current location to the boundary.