Rather than placing a landmark at each ledge, consider adding an invisible sprite attached to the lower front of your actor to detect ledges. Place it below the bottom edge and set it's position (or pin if you prefer, I tend not to use pin as much) relative to your actor. When the detector is no longer overlapping a floor, it means a hole is directly in front. Similarly, you can set a detector above at max jump height. If the actor reaches a wall, and the detector is not overlapping the wall, the actor could jump instead of turning around.
Using detectors on your actors is a great way to build logic without using too many objects all over your levels.