I've done the singing Xmas songs to be let go thing too! It's pretty funny and kind of nice to leave someone with the thought we are still human too.
When we caught another officer sleeping at night in the unit we'd get some black paper and tape it to all the windows then wait and see what he does. He usually starts by turning on the healights, but to no avail:):)
Here's the story, our Cal Trans workers usually work in the middle of the night so's to avoid all the traffic problems during the day with road closures. Well, our department assigns officers to work OT with the crews at the beginning of the closures so they can makes sure people don't crash into them. We had a unit that was assigned to do this and what the guy did was park at the start of the closure. The partner walked about an 1/8 mile back to the workers and told them that they were there but to make sure the workers didn't come over to their unit because they had a police K-9 in the car and it would attack. The workers agreed and the officer went back to the unit. At the end of the shift, the Cal Trans guys wanted to clean up and leave but they couldn't get a hold of the unit. They called a Sgt and told him what was going on. They told the Sgt that they were afraid to go near the car because of the dog. The Sgt, knowing the officers, went over to the car and found both of them asleep, and the K-9 was really one of the officers own dog! BUSTED!:)