BoA Characters are getting interesting and intelligent I see. But I can only give one solution...
You should try making the background transparent. Or, use the same cliff texture on the areas you want to use the ladder script. (Say, Ladder script placed on Stone cliffs every time). This may work. But the repetitive texture might make it uninteresting.
Or, you can make the ladder a puzzle object. Make a special encounter which asks for a ladder. Then if the player agrees the condition. It will deduct 1 ladder from the inventory, execute the script, draw the ladder and DONE.
And I suggest not to give freedom to players to use it at their own will. They might goof around with cliffs and your scenario may start glitching up.