Or just not have 'contactless' cards in the first place.
Remember: should you experience card fraud, provided you report your card lost or stolen or misused, and you have not acted fraudulently or without reasonable care, you will not be liable for any fraudulent transactions.
Don't most contactless cards have a limit per transaction? I use mine on my debit card to get my lunch in Boots (only £3.79).
On another forum, someone claimed a contactless debit card was debited despite presenting his Freedom pass to a London bus Oyster reader. The system is supposed to refuse cards when more than one is detected.