well if you spend your bitcoins you still pay taxes to some extend so I guess you cant avoid it but as its a decentralized system nobody should be able to see unless you get huge ammounts of money on your bank account out of nowhere. So selling your bitcoins for cash would be the best solution unless you have huge amounts of bitcoins but somebody who has huge amounts of bitcoins knows how to turn them to cash. In my country you need to hold your cryptos 1 year after that they are tax-free but I dont know how they do it with altcoins as most of them are not exchanged for cash but for btc and I dont know if I would need to hold those exchanged btc another year or not...