I picked up a Precision Design GP-1 GPS Geotag Adapter Unit & Shutter Cord for Nikon Digital SLR Cameras from Cameta Camera for $49.95. Comes with a couple of cables to fit nearly all Nikon DSLR's and a shutter release cable to boot. The unit appears well made and fits in the hotshoe or you can attach it to camera strap, etc. It has an LED to tell you what the status is as well as on 'On-Off' switch so it won't drain the D600 battery when it is off. (It uses camera power even when the camera is powered off, so be sure to disconnect the cable or turn the unit off or it will drain the battery.) I went on a 3 hour hike with the unit on the entire time and it worked like a charm! All my photos were tagged with latitude, longitude, and altitude which LR4 picked up right away! It only took a minute or two to go active and stayed active the entire time. For $49.95, it seems like a very good deal.