A metal wellbore tubular wall of a wellbore tubular, having a cable system arranged on an outside thereof, is to be perforated downhole. The cable system contains a fiber-optic cable, and a magnetic-permeability element with a relative magnetic permeability μr,m of at least 2,000, such as an electrical steel, is configured along a length of the fiber-optic cable. The cable system is located by sensing the magnetic-permeability element through the metal wellbore tubular wall, using a magetic orienting tool which is being lowered into the wellbore tubular. subsequently, the metal wellbore tubular wall is perforated in a direction away from the cable system.