What other choices? Fort Campbell is not so hot.
My pick might be Fort Carson in Colorado.
Ft. Huachuca, AZ
Right now they are in the middle of the transborder visitors but there is not enough there to give them a reason to hang around.
If you like the outdoors, lots of wonderful national parks, history and touristy places close by (Tombstone 30 minutes)to occupy your idle time.
Excellent choice. He'd get hiking in the mountains in the summer, skiing/boarding in the winter. Denver is not too far away if you want something from a big city. Colorado Springs is a very military friendly town. There are something like 300 days of sunshine a year, low humidity, moderate temperatures. The four corners (where-ever they are, really) and the Mesa Verde area are not too far away. Royal Gorge very close, Santa Fe not too far away. Even the Grand Canyon is only a day's drive. Vegas a long day's drive. White Sands NM, Roswell NM, all within driving range...