I have some problems with the phrase "a wolf in sheep's clothing" - some serious, mental problems. That ridiculous saying is draped in flaw. I've seen a lot of sheep in my life, all over the world, and not a single one was ever wearing clothes... not even so much as a hat. Unless there's a cult out there somewhere that dresses farm animals in people clothes, I can safely assert that all sheep are naked all of the time.
A sheep whose wool has been sheered appears to be more naked than a wool-covered sheep, but neither of them is "clothed." If you shaved all of your dog's hair and covered yourself with it, you wouldn't say you were wearing your dog's clothes... you would say, "I'm a disgusting individual with no foreseeable hope of marrying." You wouldn't have to say that, though. People are intuitive about things like that... they would know.
So what have I drawn here? A sheep in wolf's clothing? Come on - let's call it what it is... a "sheep under wolf's carcass." It doesn't sound as charming, but accuracy trumps eloquence. Hey, look! I just found a worse saying!