(Defenses) If it relates to the king or the ruler and his army in the dream, a trench then means one’s men and wealth.
If the trench relates to a scholar in the dream, then it represents his advisors, or his circle of intimates who support his theories.
If it relates to one’s wife, the trench then represents her guardian or her father.
If it relates to one’s son, the trench then represents his parents. Noticing a city without a trench or a castle to defend it in a dream means failure to pay alms or charities, wasting money, losing knowledge, the spread of evil, or an enemy attack against that city.
To see a trench in your dream signifies that you need to be cautious around strangers. Someone treacherous is out to do you no good.
An evil influence is near you; do not be entrapped.
A dream denoting siege and triumph over resistance (Old Dream Book).