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.
(..) we've always been satisfied. That's exactly why today is going to be very hard for me. I hope you'll excuse my mood. My man was killed right here on your turf. The Chinks tell me that the hit man... was kind of the Italian type. So we figured that Tony might know something. (..)1994 Léon: The Professional