An idea:
What if each Skin has a different place they can't enter, and trying to enter it requires that they Stay Calm?
So, Vampires can't enter direct sunlight, Mortals can't enter a monster's dwelling for the first time, Witches can't enter hospitals, etc.
To do so requires that you Stay Calm, and you run the risk of freaking out, attracting attention and giving yourself away. Oh, and the risk of sparkling, obviously.