[tehwebguy]

I like the pump check idea you mentioned.

Every morning just check each pump. Pretty basic stuff and that would mean easy-to-discover skimmers never sit for > 24 hours. You could then assign liability to undetected skimmers after a window of time.

[shiftpgdn]

Gas station workers probably don't have the technical know-how to spot a skimmer.

[netsharc]

Open known-clean pump. Take picture of inside. Give picture(s) to worker, tell him to look inside every day and compare to picture(s). If the inside of the machine doesn't look like the picture, call manager, and put "Out of order" sign on machine.