Mrs Claus,
Last year I had a Cav unit requesting the Garmin Foretrex 201. This is a rechargeable GPS that's worn on the wrist. You would also need to get a vehicle charge adapter if it's not included (it wasn't when I bought it). If your son he thinks he may be where he can not always recharge somewhere every 10-15 hours, you might want to consider the Garmin ETrex Legend instead. It's probably not as nice and definintely not as convenient as the Foretrex but it runs on AA batteries.
You'll need to plan on replacing any GPS after about 3-4 months. The dust and heat are very hard on electronics
update:
I did a little research and the only GPS being requested by name this year is the Garmin Rino, BUT this unit transmits location. The GPS unit on the List of Things Needed with AmericanSnipers.org is the Garmin 12 Series, BUT this unit has been discontinued.
The Foretrex is NOT a mapping unit. The ETrex Legend IS a mapping unit. The mapping features are nice but personally I still always check my coordinates against a paper map anyway. In my experience, the first sign that a GPS unit is failing is that it will give incorrect coordinates and/or distances traveled (I noticed disagreement in distances traveled before disagreement in standing coordinates). It's a good idea for any group to have two GPS units so they'll know if there's a problem before they end up in the wrong place. Mark your calendar to send a replacement instead of waiting for him to ask.
You and your son are in my prayers.
jo