You can't change the rules mid lease, specially if you have allowed smoking. 1. Put it in the lease.2. Provide an alternative defined smoking area. 3. Inform all move-ins that you are transitioning to a smoke-free community and new leases may not smoke in their units. 4. Have all renewals agree to the no smoking policy. 5. Begin soft enforcement. Typically if i get a complaint, I post a notice on all doors stating "During our transition to smoke-free, it is still a violation of the lease to disturb the neighbors (obviously written better than that), If you are aware of who is smoking, please notify the office." Post that on all doors in the area, even the person complaining. It shows that you are responding, and puts the smoking on notice that you and the neighbors are watching. 6. After enough time has passed, and everybody is on the no-smoking lease, then continue with a version of the notice above and stricter enforcement.7. when asked what the smoking policy is, just state "Same as [insert your city name] laws, no smoking with # feet from any doors, windows, or air vents"