The way I understand it (and please correct me if I'm wrong, everyone) is that you want to have your BTC in smaller parcels, and not on exchanges preferably. Also, send it around to yourself, using always a new generated address, which blurs your tracks.
At some point in the future, the government may come knocking on your door, and you may find yourself faced with capital gains tax - but only from that one parcel that you used for the fiat/BTC deal.