Just to reiterate, wouldn't the the real key be needed to come onto the field first to make sure the shield stays up? Nevermind if the keys look alike, three creatures cannot be spawned at the same time if they occupy three different spaces. So, technically, the opponent can follow which one the real key is by finding out which slot the next creature was supposed to come into, assuming, of course, the shield has a 100% chance of staying up on your turn since the real key will make it out onto the field first then followed by the fake ones.