I've thought about this a million different ways and I'm still not really sure what I would do. On one hand, I absolutely hate HATE hiding anything. Anything I've ever tried to hide in the past never failed to rear it's head at some point, so I've learned my lesson on that. Plus I have an awful memory and if I just tell the truth, I don't have to worry about remembering anything.
Just recently, the girl I've started talking to went into my closet (on my request to look for something) and I admit some stuff wasn't well hidden. She came back with a different attitude temporarily but never said anything else about it. I almost want to hope that she just didn't see pins and assume the worst. This is a casual girl and I'm not really sure if we'll ever be anything serious, so there's no way in hell she needs to know. But what if she just asked me, face to face? She loves the muscle (and veins), so for all I know she may just assume I'm on them, anyway. I honestly don't know what I'd say. That's just my personality, though. If I'm lying to protect someone else, that's different, but odds are I'm going to either be straight up with you or just tell you it's none of your business.
A wife, assuming I ever get married? Depends...nothing wrong with a trusting marriage, but would she really understand what you're doing? Is she going to freak out and every time you get into an argument she accuses you of roid rage, or worse, uses it against you legally? Guess who has the upper hand on that one in a court of law...