Are your counters a bit worn making it easy to tell the difference between a face-down Intruder, Lab Animal, and/or Dummy counter? Or maybe you just have a keen eye and see the red of the intruder counter reflecting off the mapboard. Here is an alternative to using those face-down counters on the map sheet and using "unknown" tokens instead. The "unknown" tokens can be anything really - question-mark counters, blips, little green discs, or little wooden cubes - the goal is to remove the face-down counters from the map so you don't have a clue as to what you are getting into. See file for details.