Doing a little research, it's possible to find interesting candidates (as opposed to old retreads that coach on the offensive side of the ball) working for schools in which State would be a pretty obvious step up in terms of prestige and money. I think these are three interesting candidates that I would want to talk to if I were Mullen. Of course, if I were Mullen my contact list would be full of good d-coordinators to call.
Tim Banks - Central Michigan, DC - 15th ranked D in the country in 2009, very young (coached at UCM and Maryland - never coached in the south)
http://www.cmuchippewas.com/ViewArticle.dbml?SPSID=46374&SPID=4199&DB_OEM_ID=10500&ATCLID=748560&Q_SEASON=2009
Dave Huxtable - UCF, DC, been around a while - coached with O'Leary at GT too
http://ucfathletics.cstv.com/sports/m-footbl/mtt/huxtable_dave00.html
Greg Hudson, ECU, DC - most of his jobs have been up North - Minnesota, Cincinnati and Connecticut before ECU (not sure about recruiting)
http://www.ecupirates.com/sports/m-footbl/mtt/hudson_greg00.html
Tim Banks - Central Michigan, DC - 15th ranked D in the country in 2009, very young (coached at UCM and Maryland - never coached in the south)
http://www.cmuchippewas.com/ViewArticle.dbml?SPSID=46374&SPID=4199&DB_OEM_ID=10500&ATCLID=748560&Q_SEASON=2009
Dave Huxtable - UCF, DC, been around a while - coached with O'Leary at GT too
http://ucfathletics.cstv.com/sports/m-footbl/mtt/huxtable_dave00.html
Greg Hudson, ECU, DC - most of his jobs have been up North - Minnesota, Cincinnati and Connecticut before ECU (not sure about recruiting)
http://www.ecupirates.com/sports/m-footbl/mtt/hudson_greg00.html