I am searching for plot markers using a metal detector. I need to walk parallel lines in areas where the plots might be located and want to be sure that I don't wander over areas that I already walked or too far from previous lines. What would be ideal is to be able to track my route and then give an auditory signal if I am getting too close or too far from a previous walked line. I have a Trimble DA2 receiver so location accuracy is pretty good.