Well, the same question for how do you keep a good HC long term once you find one. We used to have legendary coaches like TO, Switzer, Bowden, Paterno....etc that stayed at programs a very long time.
Now, you either have HC that think they need to jump around every 4-5 years or fan bases that think all coaches need to be fired about that time instead of letting coaches that have had some success, but maybe lost a few games, work to maintain a program and keep improving.
It's one reason why OSU fans wanting Day fired is so stupid, just because he's lost to Michigan a few times.