As a noun patrol
is (military) a going of the rounds along the chain of sentinels and between the posts, by a guard, usually consisting of three or four men, to insure greater security from attacks on the outposts.
As a verb patrol
is to go the rounds along a chain of sentinels; to traverse a police district or beat.
As an adjective unpatrollable is
not patrollable; that cannot be patrolled.
As adjectives the difference between patrollable and unpatrollable
is that patrollable
is capable of being patrolled while unpatrollable
is not patrollable; that cannot be patrolled.