PATROL

[verb] -ll- - (esp. of soldiers or the police) to go around (an area or a building), usually regularly, to see if there is any trouble or dangerThe whole town is patrolled by police because of the possibility of riots. [T]A security guard with a dog patrols the building site at night. [T]Coastguards found a deserted boat while patrolling (along) the coast. [T; I + preposition]