When Mark Richt replaced Jim Donnan, he stayed. When Brian VanGorder left for the Atlanta Falcons, he stayed. When the rest of the defensive staff got pink slips, he stayed. But now, Georgia's assistant head coach and defensive line coach Rodney Garner is leaving to take the same job titles at Auburn.
Both Garner and his wife are Auburn alums, and that's ostensibly the reason that he's making this move. I've not heard of any discontent regarding Garner and the school or the other assistants in Athens. I also am not aware of any past history between Garner and Gus Malzahn, as the latter was merely a high school coach in Arkansas before joining Houston Nutt's staff in 2006.
Garner must have just figured now was a good time to move on after 14 years on the job at UGA. Some guys just feel the need to take on a new challenge after a while, and it's hard to fault a guy for wanting to go to his alma mater.
The timing of the change is not ideal, though. Garner was Georgia's recruiting coordinator, and we're getting into recruiting crunch time when schools need to retain their commitments and close on the undecided. The article I linked to above goes over a lot of the details on that.
Garner will work under former Southern Miss head coach and South Carolina defensive coordinator Ellis Johnson, who Gus Malzahn hired to coordinate the defense. It's likely that Garner will be the recruiting coordinator there too, and he might be the biggest short-term impact according to an anonymous former SEC head coach. It's not often that sub-coordinator assistants moving around is big news, but this qualifies.