Well, considering that most of them were taken into custody on the battlefield actively engaging in hostile activities against coalition troops (not just US soldiers), I think the "deep-six" option is a viable one....though I'd more strongly support a "20,000 leagues under the sea" relocation....
Odd, the DoD doesn't seem to agree with you. Allegedly roughly 775 detainees have been sent to Gitmo. Roughly 420 have been released with no charge. Roughly 270 detainees remain. 20% of remaining detainees are cleared for release, but their home countries don't want them back.
3 detainees have been convicted of crimes. The US eventually intends to charge a total of around 60 more detainees.
Granted, the next bit is entirely hearsay. Folks I still talk to from ye olde Army days explained to me that many (maybe most) detainees were handed over by third parties in exchange for reward money. This has netted us some real high value intelligence. However, it has also netted us a very large number of people who were not guilty of much if anything, but primarily the captors wanted the reward money and invented stories. The other supply of detainees handed over by locals are results of personal or clan grudges.