On a side note I live next to one of the only cemeteries that I know to have no fence or wall all the way around. One of the sides is completely open.
Then move - NOW! Before they get you!
Back on topic, if you look under veils in Your Story will find a bit on boundaries - how a veil is contained by defined by boundaries.
Thresholds are generated by someone living in an area (apartment, house, cave, etc). Often they are weak (i.e. a bachelor like Harry who lives alone) but they exist where people sleep.
there's a brief bit near the end of GS and the problem caused by some of the bad guys sleeping at the lair.
. Holy ground has something that's close enough to where people live to called a threshold. Where no threshold exists a boundary can be established and a Ward tied to that (instead of the threshold).
I've looked though the books and various WoJs and I have seen anything in the setting as written that says other types of thresholds exist - but if people want to modify the setting, that's great. I can see a narrow strip in the food court, the one between McDonald's and Burger King, becoming a boundary like that.
Of course, I could have missed something. Some WoJ or some reference in one of the books. If it's out there then maybe one the keepers of the WoJs will parachute in an enlighten us. It's happened before.
Richard