The Collaborative International Dictionary of English v.0.48:

patrolling \patrolling\ n.
   The activity of going around or through an area at regular
   intervals for security purposes.

   Syn: patrol.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Patrol \Pa*trol"\, v. i. [imp. & p. p. Patrolled; p. pr. & vb.
   n. Patrolling.] [F. patrouiller, O. & Prov. F. patrouiller
   to paddle, paw about, patrol, fr. patte a paw; cf. D. poot
   paw, G. pfote, and E. pat, v.]
   To go the rounds along a chain of sentinels; to traverse a
   police district or beat.
   [1913 Webster]