According to what I've read about the history of how the U.S. acquired the right to use this slice of Cuba for its own purposes, it appears that the original lease stipulated:
"(a) The area must be used only for a coaling and naval station."
Guantanamo Bay has been occupied by the U.S. since 1898. Since they are clearly using it for purposes beyond those sanctioned in the original agreement, it should technically become null and void, or at least it seems so. If there are any lawyers who I've caught reading this, please send me a message in the msg board to the right & help me to understand the legal logistics of this thing!