1. A navigation system for determining a position of a sensor relative to a portion of an anatomy including soft tissue, comprising: a localizer configured to produce a field relative to the anatomy; a tracking sensor for sensing the field produced relative to said tracking sensor to determine a position of said tracking sensor in the field; and a housing including said sensor; wherein the housing is configured to allow movement of the housing relative to the soft tissue when affixed to the anatomy subcutaneously; wherein said localizer includes a mobile localizer configured to be moved by a single hand of a user and configured with said sensor to determine the position of said sensor relative to the anatomy, the mobile localizer defining a field steerable by the user relative to the anatomy.