You need to explain how you add specific value to that organisation and the detremental impact on its efficiency if you were to be moved. Also include any 'special' needs e.g medical/social/resettlement/housing etc as appropriate.
Be Warned Though! noone is irreplaceable and the needs of the service come first no matter what your boss might say after all your post maybe a gucci post for up and coming thrusters and they might not want you settling into your retirement there.!