He is right: it is his property, and he has the legal right to smoke on his own property even if it affects or inconveniences neighbors: anyone may do anything on his property which is allowed by the law, including local zoning, housing, health, etc. ordinances. Unless you can find some law which he is violating--and there is no statewide ban on smoking on your own property, so you'll have to look at your town/city's laws--he may do this.