I'd like to offer an example of one of my boundaries to illustrate what other vets are trying to say here.
As a nonsmoker, I don't like smoke around me. At my house, friends and other visitors know not to smoke in my house. However, an ashtray is readily and clearly available to them outside on the porch where the deck furniture is should they elect to smoke while visiting me. It is available to them and I'm not controlling them at all. They make a choice to smoke outside or not. Simple as that.
In no way am I taking their choice to smoke away unilaterally. See?