That's already an issue for Doug Marrone -- or any head coach entering his second season -- but exacerbating the problem is timing. The music is about to stop for the coaching version of musical chairs that takes place each January, leaving fewer options on the market.
Here's some of the more notable names that the Bills could sift through as they attempt to fill their vacancy at defensive coordinator:
Jim Schwartz -- Fired by the Detroit Lions, Schwartz has a defensive background. Like the Bills, the Lions had one of the NFL's best defensive lines last season. He runs a more traditional, 4-3 scheme than Pettine but he could be the best option to take advantage of the talent along the Bills' defensive line. His long-term future in Buffalo would be murky, as Schwartz is a veteran coach who could jump at the chance to become a head coach again.
Greg Schiano -- Like Marrone, Schiano comes from a Northeast college background. Unlike Marrone, Schiano came up through the ranks as a defensive coach and could potentially create an ideal pairing with the second-year Bills coach. What's not known is what sort of relationship the two coaches have, and whether Marrone would be willing to bring Schiano's controversial coaching style onto his staff. Several former Tampa Bay Buccaneers players have spoken out about Schiano's hard-line tactics.
Wade Phillips -- Phillips is perhaps the most experienced NFL coach without a job. He served as Bills defensive coordinator from 1995-1997 and head coach from 1998-2000. After being fired, Phillips was in a dispute with Bills owner Ralph Wilson over the final year of Phillips' contract, which the Bills were eventually forced to pay. It's unclear if Phillips would want to return to Buffalo, and even if he did, Phillips' 3-4 scheme would be an adjustment for the Bills' defensive personnel.
Gregg Williams -- Phillips' replacement in Buffalo, Williams spent three seasons as the Bills' head coach. He hasn't received a head-coaching job since and his stock dropped after a one-year suspension as part of the New Orleans Saints' bounty penalties. Williams spent last season as a staff assistant with the Tennessee Titans. Would the Bills want him back? Would he want to return to Buffalo? That's unclear.
Eric Mangini -- After two seasons away from coaching, Mangini returned to the NFL last season as an offensive consultant for the San Francisco 49ers. Mangini served as head coach of the New York Jets from 2006-2008 and the Browns from 2009-2010. While Mangini would likely consider the chance to progress back up the coaching ladder in Buffalo, his scheme may not fit the strength of the Bills' personnel. While in New York and Cleveland, he ran a traditional 3-4 system that requires a hefty nose tackle and outside linebackers with some coverage ability. Both would take away from the strengths of Marcell Dareus or Kyle Williams (at nose tackle), as well as Jerry Hughes and Mario Williams (at outside linebacker).
Steve Spagnuolo -- Spagnuolo's stock rose after the New York Giants won the Super Bowl in February 2008. He became head coach of the St. Louis Rams a year later, was eventually fired, and later served one season as the defensive coordinator for the New Orleans Saints. He was a senior assistant for the Baltimore Ravens last season and is surely looking to get back on his feet as a coach. Like Marrone, Spagnuolo has ties to colleges in the Northeast. He also runs an aggressive, 4-3 scheme that could maximize the talent of the Bills' defensive line in the pass rush.