Spikes overruled

We all have gardens between the 2 building-blocks I and my back-door-neighbours live. These gardens are not accessible without key's and the doors and parts of the walls are equiped with spikes to keep-out burglars.
One of our backdoor-neighbours have put a bar above these spikes for their plants to grow.
However I don't think their upstairs-neighbours will be very pleased if somehow someone climbs on their balcony.