You can't keep other candidates from 'poaching on your turf'. [=from trying to get voters who usually vote for you or your party to vote for them]
In chapter two, the author is on unfamiliar 'turf'. [=is dealing with an unfamiliar subject]
Synthetic 'turf' was installed in the playing field instead of grass.
(..) you're going to remember me this time. You are so busted. This really doesn't concern you. Well, actually, Janine is senior drive-thru manager, so you are on her turf. So, this makes sense. - Oh, Lester... - I want you to be happy. Would you like Smiley Sauce with that? (..)1999 American Beauty