Let's say a miner spots a diamond. He may glance around to make sure that security guards are looking the other way, and press the diamond under his fingernail for later transfer to another receptacle, such as his mouth. In the event that members of the security force have been corrupted (always a possibility), he needn't be that careful. The next step is to get the diamond out of the mining area. In one scheme workers smuggle trussed homing pigeons out to the mining areas in lunch boxes. They fit the birds with harnesses, load them with rough, and set them free. Sometimes the thieves are too ambitious. Security officials at Namdeb caught one thief when they found his pigeon dragging itself along the ground, its harness loaded beyond takeoff capacity.
Another time a thief smuggled in the pieces of a crossbow, later sending a volley of hollow bolts freighted with diamonds arcing over the fence, for retrieval by a confederate. This scheme ended when an unlucky shot fell to earth in front of a security jeep. Diamonds are dropped into the gas tanks of machinery leaving the beach, and inserted into razor cuts in tires; collaborators remove them later. Miners wedge diamonds behind sweatbands, tap them into ears, and insert them in other orifices. At one De Beers mine, security guards caught a thief only because he'd inserted so many gems into his rectum that he was waddling. Diamonds fluoresce under x-rays, and Namdeb uses x-ray scanners on employees leaving the mining area. But as miners well know, the cumulative health hazards posed by x-rays dictate random use. The scanner always makes a noise, but it is not always taking an x-ray. So the miners take their chances, and diamonds slip through.
http://www.thievesguild.cc/articles/diamond/