Hey Nancy,
In Modesto, before smoke free was a thing in California, a client agreed with my suggestion to go smoke free in a couple of buildings. Once we started with those buildings, it was easier to just go smoke free in whole community. There were no addenda forms so we created. These were B properties and we expected blow back. Quite the contrary.
Here's what we learned - if you take away an area to smoke, you MUST give another area because smokers are going to smoke so they will stand outside the building annoying residents and tossing the butts.
Extreme fines are necessary and the leases stated they would be evicted for non compliance on the second fine.
Back to the area - our best area was partially covered by a carport, next to the enclosed dumpster area with provided butt disposal containers and a picnic table. Tried to make it nice since it WAS by the dumpster but we couldn't take a parking space.
Don't be worried - you will be so delighted with the ease of your residents adjustment!