  We consider a model in which accelerated particles experience line--elements
with maximal acceleration corrections that are introduced by means of
successive approximations. It is shown that approximations higher than the
first need not be considered. The method is then applied to the Kerr metric.
The effective field experienced by accelerated test particles contains
corrections that vanish in the limit $\hbar\to 0$, but otherwise affect the
behaviour of matter greatly. The corrections generate potential barriers that
are external to the horizon and are impervious to classical particles.
