What I do to get around that is take a picture of the GPS unit (my tablet) at the end of the run: the GPS window shows the correct time, the picture has the camera time, when tagging, it's easy to correct for the difference (and you can't forget to set the camera time correctly)
Does the 5D III allow audio files to be recorded and connected to the Image. That way you could state the information regarding location etc. However, unless you are doing some type of scientific or legal oriented project I don's know why you would need the specific map coordinates. Just a quick identification like "Ruined gasoline station along old Route 66 West of Albuquerque N.M."
Some of the Professional 1D (series cameras can include audio files). I really think that the 5D and 7D series of Canon DSLR cameras should also have had that capability. I have a 1995 era Olympus 5050Z P&S which allows audio recording for information regarding images.. It was really handy on a trip to Rocky Mountain National Park...
You can use the 5D III to document what you are shooting by shooting a video clip (using lowest quality format) of the scene and record your description. Using the lowest quality video will save space.
I have used this technique when shooting a group of models. I shot a video of each lady and asked her to state her name and spell it on the video and spell out her email address.
A plain old pocket tape recorder or a newer digital recorder is another very efficient way to take notes.
BTW: On trips with a guide, it might be worthwhile to videotape the guide's explanations and descriptions. I wish I had thought about that during my trip to China. One day we hit four cities and I couldn't remember in what city we had eaten our evening meal
I like your idea of the audio. I do have a compact digital voice recorder, and have used it when guides were around. It's good to jog the memory as well as concentrate on the shot and not so much on notes. Thanks for the tip.
My daughter gave me a Canon GP E2 for Christmas a couple of years ago. I was a bit hesitant about it's usefulness until my wife and I went on one of those crazy "see Europe in 25 days" bus tours. After three weeks of jumping on and off the buses and trains, taking photos in towns and cities with strange sounding names we were exhausted and totally confused as to where we had been.
It is good to be able to reflect now and see where we were and where each photo was taken.
It works well in Lightroom, showing where each photo was taken on a Google map. It is compatible with my old Canon 7D and works equally as well with my Canon 5D Mkiii.
They are expensive, but I think they are good value