For sites with lengthy perimeters, consider some form of drone flights for checking on the security of fence or boundary lines. This renewed awareness arises from a Government Security News post on how BNSF Railway is using unmanned aircraft to monitor its trackage.
In the first day of operations on October 25, the ScanEagle system “provided real-time video covering 64 miles of the 132-mile stretch of track BNSF has designated for the exercise. ScanEagle is capable of flying for up to 24 hours at speeds of up to 80 knots.”
(BNSF, incidentally, is a combination of 11 U.S. railroads including the Great Northern, Santa Fe, and the Burlington Route. Remember them?)