  We propose a new mechanism for explaining the very long lifetime of
superheavy dark matter X, which is proposed as a source of the ultra
high-energy cosmic rays above the GZK cutoff (5 \times 10^{19} eV). The singlet
X particle couples to the MSSM particles only through a bulk singlet field
which develops the v.e.v. in the ``hidden'' brane. The distance between this
hidden brane and the ``visible'' brane naturally leads to the exponential
suppression of the coupling. The X particle decays predominantly into the
higgsino and higgs boson of the MSSM, and its decay spectrum is completely
determined once their properties are known.
