Alright, so I know I don't play much anymore, but I had a thought.
As you guys already know, when you toggle your plot to allow others to break and build, be it for a job you are hiring them for, or other, it also means that they can break armor stands(Possibly with your hard earned armor on it to show off to the world:P) and chests that don't have the shop sign on it.
What about implementing something like structure block (already in 1.10)? using the corner blocks, you would be able to outline certain areas that you don't want your employee to be able to break. basically like plot protection within the plot......
I'm not sure how it would work, but I'm sure that it could work with the right pluggin!