My friend has just phoned me really upset as she has noticed that her neighbour has placed broken glass all along their dividing fence at the back of the garden. There is no issue between them, she does not really know them but she thinks that it is to stop the cats walking along the fence and possibly to deter the cats from going into her garden. My friend has one cat but there are a few other cats around which walk along the fence. Does anyone know if the neighbour is allowed to do this?