Mo. Rev. Stat. § 452.1220

A deploying parent, by power of attorney, may delegate all or part of custodial responsibility to an adult nonparent for the period of deployment if no other parent possesses custodial responsibility under law of this state other than sections 452.1200 to 452.1258, or if a court order currently in effect prohibits contact between the child and the other parent. The deploying parent may revoke the power of attorney by signing a revocation of the power.