The guardhouse increases the protection against sabotages and espionage of both Military and Economy in yourcastle/outpost. The higher the level of the guardhouse, the more guards there are and the harder it is for enemy players to sabotage and carry out espionage on the castle. Players aren't limited to just one guardhouse per outpost, they may build as many as they wish; the only limitation is space. Everytime a guardhouse is built or upgraded, that castle will gain 5 more City Guards. The more agents your enemy sends, the less risk of capture. The passive ability to prevent spies from scouting defensive layout, has a cumulative effect with additional guardhouses.