Many moons ago when doing the application part of a 9-month dispatchers course, was surprised to find a take-off restriction (obstruction) in an exercise when departing CPH 04R with a B767. To wit, there's nothing but 15 NM of water separating Denmark from Sweden. The instructor knew what was coming, and went to great lengths explaining how obstacles does not only come in form of of fixed buildings and geography, but also moveable objects. In this particular case it was the USSR school ship "Kruzenshtern", which had quite a magnificent air draft from her 3 masts - just over 50 meters if memory serves me right.
For the exercise in question this restriction would come into play, resulting in a payload reduction to meet the
SEO performance criteria. A clever sod in the class, however, submitted a solution with no payload reduction. When quizzed by the instructor, he said a simulated call had been made to the tower, asking them to have a look-see if the ship was indeed anywhere near. Since it wasn't, he surmised the restriction was not valid and proceeded accordingly. His solution was accepted and commended, in an effort to make the rest of us consider "thinking outside the box" and learn a valuable lesson.