My husband is early stage, so what I've done is explain why we have to be especially careful with a debit card, as opposed to a credit card; and that we don't want to lose it because we don't want someone to gain access to the bank account(s) behind it. He still understands these things. So we literally keep the debit card in a safe (which he can't open) and I only give it to him when we go to the bank to get cash, then I put it away again when we get home. Eventually, he'll get to the point where he forgets about it; and it will be in the safe.