[zmimon]

It seems to me that the right approach should always have a significant random element, not as a deterrent, but as a check on how well the non-random component is working. The random part will examine in depth to find anything that should have been found in the non-random part but wasn't (say, body searches to find large metal objects making it through the x-ray screen at the airport). Without that you would be blind to defects in the system.