If she lives in another state and its a one time thing, then I wouldn't care but otherwise I don't want everyone in town knowing so I suggest being extra careful. I think its possible to get very close to being undetectable but I don't believe you can get it 100%. I have always believed that it was the best thing to go ahead and tell them if and only if you planned on being in any kind of relationship. If your hair looks good and she likes you, she won't care. I've had to tell a few girls before and none of them cared one bit. It's a relief when they know and you don't have to worry about them finding out the wrong way. Luckily I don't have that problem anymore. I know there are others that disagree as this has been discussed before, but i am just giving you my opinion mate.