My 22 year old moved back home and smokes. Any advice for how to set rules?

A week ago our 22-year-old son moved home after living on his own for 5 years--4 at college and the past year in a house with several roommates that became a bad situation (lots of drugs in the house). My husband and I heavily persuaded him to leave that group behind and move back with us. We had gotten quite used to being empty nesters as our other children are in their late 20s and early 30s and have been gone for years. My son is working full-time in a low-wage position and is still trying to figure out what he wants to do long-term. We're having him pay us a small amount of rent, well below what it would cost him to have his own place in our city.So far everything is going well for all 3 of us adjusting to our new living arrangement and our son is mostly going out of his way to be deferential and helpful around the house. The one problem we have is that he's a cigarette smoker and now uses our back porch as his place to smoke. I know there's nothing I can do to make him quit, but I hate the smell of cigarette smoke and don't like that my husband and I can't escape it in our own home. Our house is on a 1/8 acre lot so there's really no way to enjoy our porch or backyard, or have the windows open, without getting the smoke whiff. He always smokes first thing in the morning when we're getting ready, and then several times after dinner.I'm struggling with what to do. My son knows we don't like the smoke and is respectful of us, but I don't want to kick him out to the street at night. We really dangled the carrot to get him back here into what we think is a better living environment for him and promised him we'd treat him like an independent adult instead of a child. I don't want to do an about-face so quickly but am wondering if I'm being too much of a pushover.TL;DR: Should I let my adult child smoke on my property? via /r/Parenting http://ift.tt/2wwNAs7