When I was in, we used to find units on an ARTEP or something that thought they were on a vacation and give the perimeter guards a smiley face with a permanent marker on their.....necks. This way you always knew who wasn't paying attention on guard or who had fallen asleep. Man that would piss some people off. We always loved our brass coming down, and grinning and saying that official policy was that we would not be participating in these activities...and that any one caught doing them would be subject to company punishment. Needless to say it didn't stop and that certain units were far more alert on training exercises than normal...as they should have been....