@Jessica1528 How much longer the guest is staying would be a deciding factor for me on whether or not I said anything to them about it. Are they already gone? If so, I would let it go. If there are butts left, perhaps mention that in your review, and mark them down on following the rules.
Fining people for behavior isn't enforceable on Airbnb: you can only charge for actual damage, so I would just take that part out of the equation.
If I were you, I would make sure you're reminding people of this rule before they check in and in your welcome message. Most people think that "no smoking" just means no smoking indoors, not no smoking anywhere on the property. I know you lay it out in your rules, but few guests review the rules in any detail before booking. Perhaps even consider putting up a sign at the entrance to remind people that there is no smoking anywhere on your property.