I used to use the Amprobe AT-2005. My former employer had a couple of them and they were good for finding buried boxes.
I even traced a conduit 6' deep by running a fish tape into it and tracing the tape. Found a metal water pipe for the guy who had to dig a conduit trench for us too. They were both right where I marked them at. Found a short caused by a molding nail in a traveler once too. Finding shorts was a bit trickier than just tracing conductors though. My only complaints were that at times they wouldn't discriminate very clearly. Had to try tracing from one end and then the other and sometimes it only provided a crude guess where knock the hole in the rock or stucco. I recently heard that only one of them is still working.
I had an Ideal rep talk me up at the wholesale house a month or so ago on the merits of the 61-958. It seemed to have all of the features of the AT-2005 and more in a more modern style. Cost about the same at around $900+.
