Real progress in gamma-ray line astronomy depends on the availability of high energy resolution, low background detectors. New large volume germanium (Ge) detectors have an excellent energy resolution (E/∆E ~ 500 at 1 MeV) but they do not yet reach good sensitivity for gamma-ray spectroscopy of astrophysical sources. We review the various techniques which are or may be employed to reduce the internal background in order to improve the sensitivity. We focus on the segmentation technique to reject the elastic scattering and the beta-decay background resulting from the interaction of cosmic ray secondaries with Ge nuclei. We discuss the optimization of the design of a stack of Ge detectors using Monte Carlo simulations: the operation of a multisegment detector is analysed and the influence of the number, thickness and detection threshold of the segments on the full energy peak efficiency is examined. We also compare the sensitivities of various segmentations in a particular shield and field of view configuration.