The unique idea is about the carving and you shouldn't tell this to anyone that you can't trust because that person might go through your closet and has the intention to look and copy for it.
I don't even fancy the idea of inscribing it in your wardrobe regardless of OP saying that it is dark in there. It may seem good, but that is too easy...What if someone with an idea of what "Keys" are (male or female friend) decides to one day wear one of your clothes, and makes way to your supposed dark wardrobe with a very bright torchlight?
That scene is very possible.
But since it's a wardrobe and personal place for him, I doubt it that he'll just allow someone to get in and snuck there for those clothes. I'm sure that he'll not allow that to happen.
Even though it is not advisable to save your keys in your email, i still feel if you can break them up into two or three different parts, turn them into a sort of puzzle or poem that you alone understand and save to your mail that you alone have access to, it can be really save there. You also do not need to save it to the mail address you use on our device, to increase safety, you can save to another mail address you normally do not make use of.
Well, it's like having your own pattern but I still don't think this is a good idea. I've done this before and luckily was able to read those tips about of how not ideal it is.