Mo. Rev. Stat. § 441.560
441.560 Denial of entry a defense.
441.560. Denial of entry a defense. — It shall be a sufficient defense to the proceeding if the defendant establishes that he, the owner or his agent has been unable to obtain entry to a portion of the premises for the purpose of correcting the nuisance, notwithstanding his good faith effort so to do, or that the occupants are in violation of section 441.630 .
(L. 1969 p. 537 § 7)