A riser magnet assembly having selectively removable magnet members can be incorporated within a riser assembly of a drilling rig to generate a magnetic field within a central bore of the riser assembly. The magnetic field catches falling metal objects and prevents such objects from passing beyond the magnet assembly and entering subsea equipment or subterranean portions of a wellbore without sacrificing fluid pressure integrity of the riser assembly. At least one stripper door is provided for easy access to inner portions of the magnet assembly.