I found out that the nest at my parents is not a yellow jacket nest...it's a hornets nest. And pretty much the only way to get rid of it is to spray insecticide directly into the opening and hope that you either kill them all, or that you're a fast runner.
OR - you can just wait until wintertime when they desert the nest...sounds like they'll probably just wait.
My mom is avoiding that side of the house like the plague, and they've shut gates and stuff so my neices can't get back there. I can just see one of my neices throwing rocks at that thing...HEE! They call it "the Bee's House"
Next time I'm up there, I'm taking a picture - I swear!