If a government wants to ban BTCitcoin what they will do is to force the exchanges to shut their doors and you cannot use your banking system to invest in BTCitcoin as you will leave a digital tail, these are the resources they will be using to monitor your activities but if you are smart enough and carry on trading with P2P based exchanges where exchanges acts as an escrow for the deal then it will be hard for them to follow and for an extra precaution if you can create a freelance portfolio when a question arises from where the random transaction occurs if the authorities approaches you then you are almost safe and none of the government will be able to control everything completely.