Uh.... Encryption?
http://www.truecrypt.org/ and no one will know what you have. Besides, stuff showing up on your credit card is much more likely to cause an issue anyways.
What kind of relationship are you in where you can't tell your
wife about your fetishes? I mean, this is the person you, you know, married, and who supposedly cares deeply about you.
If you're in a relationship where your SO (edit - significant other) finding out you like porn would cause strife, your relationship is fucked already.