Just looking up some numbers here is what I found for his defenses since 2007.

2016, Denver - His D was ranked 20th at 4.3ypc
2015, Denver - 1st at 3.4ypc
2013, Houston - 22nd at 4.3ypc
2012, Houston - 11th at 4.1ypc
2011, Houston - 8th at 4.0ypc
2010, Cowboys - 18th at 4.3ypc
2009, Cowboys - 6th at 3.9ypc
2008, Cowboys - 20th at 4.2ypc
2007, Cowboys - 13th at 4.0ypc

In 9 seasons, his team hit or exceeded the 4.0 benchmark four times. It looks like his average run D's are around league average.

OTOH, his overall defense numbers look much better! (don't have time to post specifics) With the exception of 2010 Cowboys, the overall yards per game his D's allowed was always in the top 10 and usually in the top 7.

Teamrankings.com is the source...