I put a variable on the "Sellimage" that keeps the tower's UID, and then, when you touch it, only the tower and the image is destroyed
example_fixed.capx
EDIT: Oh, I forgot to tell that I disabled the way you were doing... When you use the event "Is touching Object", every second that you are touching the object, the actions are executed a lot of times... So I changed to "On touched Object", that execute only once.