Columbia subject headings:
Border patrols--Canada.
Border patrols--United States.
Terrorism--Prevention--International cooperation.
Terrorism.
Harvard subject headings:
Border patrols--Canada.
Border patrols--United States
Terrorism
Terrorism--Prevention--International cooperation
Princeton subject headings:
Border patrols--Canada.
Border patrols--United States.
Terrorism--Prevention--International cooperation.
Terrorism.