Suitcases are scanned routinely and I believe that a little sticker is placed on the suitcase at the point that the offending item shows up. The sticker cannot be removed as it disintigrates. When they used chalk it was much easier as you could hand carry your suitcase to customs and rub the chalk off on your trousers.
If they are bringing a joint of pork tell them to have the bones removed as the bones shows up on X-ray.
Bacon, the vacuum packed is best.
If they are stopped and it is discovered tell customs that it is for personal consumption. Things are much more relaxed than they used to be.