Methods of defining a virtual fence and for detecting a body inside or outside a region of interest defined by the virtual fence and/or of determining a height for a body on a surface in a region of interest use radar signals and a configuration mode and a monitoring mode are disclosed. In the configuration mode coordinates for defining a virtual fence are determined and/or a topology of a surface in the region of interest is determined. In the monitoring mode, a location of a second body on the surface is detected to determine if the second body is inside or outside the virtual fence and/or a height of for the second body relative to the determined topology is determined.