  X-band ESR measurements on a single crystal of the highly frustrated
SrCu$_2$(BO$_3$)$_2$ system are shown to provide an essential inspection of the
magnetic anisotropy present in this compound. The very broad absorption lines
seem to be consistent with the largest anisotropy term, namely, the
antisymmetric Dzyaloshinsky-Moriya (DM) interaction allowed by symmetry.
However, the previously well-accepted model of only interdimer interaction is
generalized with additional intradimer DM terms. Moreover, spin-phonon coupling
is recognized as the cause on the linewidth broadening with increasing
temperature.
