Russian ships in Danish waters regularly refuse pilotage services. A reform of maritime law would probably be necessary.
But that is almost impossible to achieve. A conflict with Russia is looming – if Putin admits his role as a sponsor of the shadow fleet. The open source intelligence community could help: by uncovering the identity and whereabouts of the Shadow Ships' owners. The risk that "dark ships" pose to coastal states is heightened by the fact that they fly the flags of countries that are unlikely to come to anyone's aid in the event of an accident or incident.