Gun ports fitted to a wall of a building or vehicle each comprise an expandable aperture that accommodates penetration from within by a gun barrel having irregularly shaped attachments. The gun ports can provide protection against laser pointers used in training exercises, where lasers are used outside the gun ports by attackers against those protected behind the gun ports. Each implementation of a gun port can accommodate guns of different sizes and shapes. The gun ports can be configured as exchangeable cartridges or subassemblies that can readily replace regular non-expandable apertures otherwise used for defense against real ballistic weapons and explosives. Each expandable aperture expands and contracts as necessary to fit sizes and shapes of a gun barrel portion inserted through it. Of special importance is accommodation of a laser sensor module attached near the firing end of a gun. A window for sighting the gun is provided.