For a start, you can pretty much forget about hiding everything. It is so many ways things are tracked that the only way for it to never be discovered is to do what bettylou say – not do it at all.
Since that ain’t going to happen I like to break some other news, even telling your wife may not be enough. While I don’t have to hide anything from my wife or kids I do need to separate things a little. For example it can be somewhat embarrassing if I show some friend something on ebay/amazon/… and it shows that list of “recently viewed” stuff that would require some explanation.
The problem with incognito made and “delete *” is that you of course have to start over completely every time.
My way around it is what Emily say – I have multiple accounts. I login as a separate user that do all the cd stuff. I have separate users on all the online sites also specifically for that purpose.
I don’t use windoze so I don’t know exactly how to do it there but I do remember it being a simple way to have multiple users and switch between them with some quick keystroke, google can probably tell you everything you need about it.