This idea is mainly being able to apply the visitor buff to people on boat. And its so fresh i couldnt think of a was this could be used for malice acts so im posting here for discussion. The idea is that making special add-ons to the walls that 2 can be linked over a river to provide like a invisible gate on which the people passing from that line would get/lose the debuff. and the 2 buildings have to be connected the other way with walls. So in order for this to work you need to completely surround the lets say lake with 1 river leading out with walls. I tried to illusture it here:

So green stuff if land and blue is water obviously i even detailed the swallows.
The brown line is the wall of choice aka palisade.
The red square is the special add-on building to the wall and the grey is the invisible link between them.
Makesthat little area in the middle crime free zone.