Bring in the initial person who can run it by themselves and train everyone else. Then when they leave, promote the next guy in line, andthey start training the next people in line. Then try and retain the person in charge as long as possible before you have to promote the next guy.
Simple business strategy applied to football coaching, and I think it's agreat idea. Dan needs to keep finding people who can run the defense by themselves, and who can also be an extension of Mullenwithout him having to actually be there.