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Jack Dempsey, File, Associated Press
FILE - In this Aug. 1, 2011, file photo, Denver Broncos defensive coordinator Dennis Allen looks on during training camp at the Denver Broncos football training facility in Englewood, Colo. The Oakland Raiders' search for a new head coach is narrowing as general manager Reggie McKenzie has told some applicants they are no longer candidates and Denver defensive coordinator Dennis Allen has reportedly emerged as the leading contender.

ENGLEWOOD, Colo. — With Dennis Allen reportedly preparing to leave Denver to coach the Oakland Raiders, the Broncos may soon find themselves searching for a seventh defensive coordinator in seven seasons.

Other men who have filled the Mile High musical chair in the last six seasons are Larry Coyer (2006), Jim Bates (2007), Bob Slowik (2008), Mike Nolan (2009) and Don Martindale (2010).

The Broncos were hoping they had finally found some continuity with Allen. But the 39-year-old up-and-comer apparently impressed Raiders general manager Reggie McKenzie, much as he dazzled Broncos coach John Fox a year ago when he landed his first coordinator job after rising through the ranks in New Orleans and Atlanta.

Possible replacements for Allen could include Broncos linebackers coach Richard Smith and former Jacksonville Jaguars head coach Jack Del Rio.