  Tunneling between different topological sectors with dynamical chiral
fermions is difficult because of a poor mass scaling of the pseudo-fermion
estimate of the determinant. For small fermion masses it is virtually
impossible using standard methods. However, by projecting out the small Wilson
eigenvectors from the overlap operator, and treating the correction determinant
exactly, we can significantly increase the rate of topological sector tunneling
and reduce substantially the auto-correlation time. We present and compare a
number of different approaches, and advocate a method which allows topological
tunneling even at low mass with little addition to the computational cost.
