If there is nothing in which to 'opt-in', then the option does not have to be offered. Our Overdraft Service states that we decline ATM/POS transactions if we are able to at the point of the transaction (if they would cause an overdraft); if one of these does 'slip through' (e.g., pre-auth for gas), we 'pay, no charge'.
I hear and I forget. I see and I remember. I do and I understand.--Confucius