@Margee0, if you have a Security Deposit in place, one strategy might be to state clearly in your House Rules that if a guest violates the No-smoking rule, an amount of money will be claimed against the Security Deposit. This amount could be equal to the cost of dry-cleaning soft furnishings (e.g. curtains, sofa covers, etc.) and using special methods if necessary to ensure that bed linen, towels, and carpets are odour-free.
If you find butts, etc., be sure to take photos of them to substantiate your claim.
Another strategy would be to state that if guests - while on the premises - are found to be smoking or to have smoked - you will ask AirBnB to cancel the booking and to rehouse the guests.
I imagine other hosts here can offer tips as well.