In any action for false arrest, false imprisonment, unlawful detention, defamation of character, assault, trespass or invasion of civil rights brought by any person detained by the merchant, it shall be a defense to such action that the merchant detaining such person had probable cause to believe that the person had committed retail theft and that the merchant acted reasonably under all circumstances. (Ord. 7-15-80 § 1 (part); Code 1975 § 13-640-13.4)