Painting stolen from exhibition

At the Guildhall Exhibition in Cambridge ( see earlier blog) there was a painting stolen. It was a small work measuring only 12" x 9" and could easily have been concealed under a coat or in a bag. The usual security measures were in place with invigilators at the desk and even cctv cameras around. But with 280 paintings on show displayed both on walls and on array of screens, it was impossible to see every part of the gallery. The thief has never been tracked down or the painting recovered.
I would welcome any comments from other societies or artists who may have encountered this problem and any suggestions as to how best counteract it.