Answer: The changes suggest that the residents have gradually become more frightened and want to defend themselves.
Step-by-step explanation:
In Nadine Gordimer's short story, Once Upon A Time, the protagonist is frightened by the sound in the night and assumes that it is a thief.
As there has been an increase in crime in the suburb - houses are burgled and a person even dies, the neighbors take precautions to protect themselves. The first changes to the neighborhood are the alarm systems, but as they go off unnecessarily, they soon become useless. However, as more and more suspicious people are seen in the neighborhood, more severe measures are taken. For instance, the roses and perfect lawns are replaced by the fences and walls. These changes suggest that the residents become more and more frightened and address this problem more seriously.