  We study the quasiclassical magnetotransport of non-interacting fermions in
two dimensions moving in a random array of strong scatterers (antidots,
impurities or defects) on the background of a smooth random potential. We
demonstrate that the combination of the two types of disorder induces a novel
mechanism leading to a strong negative magnetoresistance, followed by the
saturation of the magnetoresistivity $\rho_{xx}(B)$ at a value determined
solely by the smooth disorder. Experimental relevance to the transport in
semiconductor heterostructures is discussed.
