In 2011, Christensen helped coach a unit that ranked second in the Missouri Valley Football Conference for pass defense, allowing 186.9 yards per league game through the air. Sophomore cornerback Winston Wright earned MVFC Player of the Week honors the final week of the Jackrabbits' season and also earned second-team all-MVFC honors after leading the team with three interceptions and adding 57 tackles.

Christensen came to SDSU after serving the three previous seasons as defensive coordinator at Morningside College (Iowa), where he directed a top-ranked defense that allowed only 12.7 points and 12.1 first downs per game in 2010. The Mustangs compiled a 30-6 record in his three seasons on the Morningside sidelines, allowing an average of 15 points per game as the Mustangs reached the NAIA playoffs all three years. He also assisted with the special teams units.

Christensen previously served as a graduate assistant coach in charge of the inside linebackers and later as defensive backs coach at his alma mater, Nebraska-Kearney, from 2004-08. In 2005, the Lopers qualified for the NCAA Division II playoffs and a year later ranked first in the Rocky Mountain Athletic Conference in scoring defense.

He began his coaching career in 2003 as an assistant coach at Ravenna High School (Neb.), before enrolling in graduate school.