  We investigate the dephasing rate, 1/tau_phi, of weakly disordered electrons
due to scattering from diluted dynamical impurities. Our previous result for
the weak-localization dephasing rate is generalized from diluted Kondo
impurities to arbitrary dynamical defects with typical energy transfer larger
than 1/tau_phi. For magnetic impurities, we study the influence of magnetic
fields on the dephasing of Aharonov-Bohm oscillations and universal conductance
fluctuations both analytically and using the numerical renormalization group.
These results are compared to recent experiments.
