In the story, why did the man and his wife build fences and who were they afraid of?

In the story, the man and his wife have electronically-controlled gates installed and bars attached to the doors and windows of their home in order to prevent intruders from breaking in. After hearing about the many stories of mayhem on the streets, they are afraid of the violence unscrupulous rioters could unleash on them if they do not take the necessary precautions.

As the story progresses, we get the impression that everyone is afraid. Reports of burglaries and killings are so commonplace that everyone fears for their safety. To ensure the safety of the family, the man's mother-in-law sends extra bricks as a Christmas present; the bricks are to go towards building a higher wall around the house. When the family takes walks around the neighborhood, they notice that many other homes have installed the same walls. However, some have taken the extra precaution of embedding broken glass atop cemented walls or attaching sharp spikes to iron grills.

After seeing this, the man and his wife decide that they will also reinforce their own walls. Soon, they have razor-sharp coils attached to the whole length of the walls surrounding their property. The man and his wife are grateful for this added protection, but their happiness is short-lived when their own little son becomes entangled in the coils and suffers an excruciating death. Ironically, in trying to protect themselves, they become victims of their own precautions.