The 'force field' is a reactive burst of microwave radiation triggered by motion sensors. That's not outside what we're currently capable of. (There is some scary stuff out there -- check out a History Channel Future Weapons special. And that's just what they're willing to tell us about.) As for a dome... at this point, it would have to be too big. You could cover the few blocks that make up the town, but you'd have to control the skies and hope nothing military flew over. Anything larger and you're begging for notice.
(Unless the Sponsors control the military. And satellites. Aren't conspiracy theories fun?)
At the same time, they've had too much weather to be underground... Personally, I'd stick them somewhere in northern Canada -- lots of unexplored territory, very little in the way of air travel, easy to isolate.
The bartender's an interesting spot. Assigning people to shadow Renbe's a solid idea: they know he's not pulling his nose away from their grindstone. I don't think he had any advance information on this, though -- too much investigation, and it's hard to be so supremely self-interested as to never warn your family. Or even your ex.