A marine mooring line vermin shield to prevent the passage of vermin crawling along a marine mooring line from land to a pleasure craft, including a disc with a centrally located aperture through the disc, and a slot extending from the aperture to a periphery of the disc. The vermin shield also includes a closure that is urged to insert into the disc slot in a closed state compressing the mooring line against the aperture to secure the vermin shield against the mooring line. The closure may also be locked in the closed state. The closure can also be extracted from the disc slot in an open state to allow the mooring line to be removed from the aperture through the slot past the disc periphery.