After leaving Navy, Hardin coached the Philadelphia Bulldogs of the Continental Football League, leading the team to a championship in 1966.

In 1955, Hardin was hired as an assistant football coach at the United States Naval Academy under Eddie Erdelatz.

Hardin coached Navy's two winners of the Heisman Trophy, Joe Bellino, who received the award in 1960, and Roger Staubach, who did so in 1963.

On December 17, 1964, Hardin (who had agreed to a five-year extension the previous February) submitted his resignation from Navy.

Hardin coached numerous future professional players at Temple including New York Jets defensive lineman Joe Klecko, Pittsburgh Steelers tight end Randy Grossman, Kansas City Chiefs cornerback Kevin Ross, San Diego Chargers linebacker Bill Singletary, and New York Jets quarterback Steve Joachim, who won the Maxwell Award in 1974 playing for the Owls.

The 1979 team concluded their season with a victory in the 1979 Garden State Bowl over heavily favored Cal.