Although not as portable as barbed wire, a wall of nopal cactus is a very effective fence in stopping an advancing force, in this case a curious photographer.

This photo was taken by a Hasselblad 500C medium format film camera and Carl Zeiss Planar 1:2.8 f=80mm lens using Kodak Portra 400 film, the negative scanned by an Epson Perfection V600 and digitalized with Photoshop.