I always thought Don Brown - current UMASS HC had great defenses at Michigan.
Statistically his defenses were sound. He and Harbaugh could not beat OSU though! I think he got sacrificed to apease the donors. Wasn't his fault; nobody in the Big 10 including Michigan and Penn State are on the level of recruiting that can hang with the Buckeyes. You have to imagine that guy - with some absolute studs to coach and depth to back those players up! He would have it at Clemson!