I've got to put a wifi password on my school laptops (all users are admin) but I don't want to the children see the password when you go edit conextions and edit de wifi like is see in the pictures. (I would like that you can't tick in the box Nº3, so only dots will be seen)

I would like sometihing like this that show key is like watermark so you can't see it and this screnshoot was taken in a admin acount (snox leopard osx (10.6.8) based with linux).