The last passive security feature is barriers: objects that separate frontliners from visitors especially those who are angry or hostile.

Nez Perce National Forest.

Full barriers are objects that keep visitors completely away from frontliners, such as walls with security windows. Partial barriers are objects that impede access to frontliners, such as counters and desks. A taller desk with an accessible area is best because it is more difficult for an upset or angry visitor to climb over.