Fasteners, cover systems, and related methods are provided. A fastener for fastening an item in place on an object can include a bottom member having a first cross-sectional shape and a top member having a second cross-sectional shape that is securable to the bottom member. The top member can be rotatable relative to the bottom member once the top member is secured to the bottom member. The fastener can also include a securement device for fastening the bottom member to an object. The fasteners can be part of a cover system that also includes a cover. The cover system can be used in conjunction with a window, such as a boat hatch.