In the story "Fences" Troy has still not built the fence. What might that symbolize?

You could say that the neglected fence is a symbol of Troy's neglect of his family. The fence can also be seen as symbolic of the things Troy wants to keep out, the things he separates himself from.

Explanation:

This symbolism is pretty obvious with the last dialogue we get between Troy and Cory:

Cory: "Tell Mama I'll be back for my things."

Troy: "They'll be on the other side of that fence." (2.4.110-2.4.111)

Here Troy clearly establishes the fence as a dividing line between him and his son – an actual, physical barrier that separates them. By winning the climactic fight with Cory, Troy establishes that he's still the alpha male. The fence now marks the boundaries of Troy's territory; he is still the king of the castle, and his son is no longer welcome within its walls. While the fence is now a literal barrier between the two, you can also see it as representing the emotional barrier that Troy places between them.

where is the

line a --> main

line b --> young

line c --> atitude