I am with you on that fear! I know dogs do stay, but it is a mind game, not a physical barrier. Mine are kept in with electric fencing, and I trust it completely though it isn't an actual physical barrier either, they could slip through it if they wanted, but it is physical hotwires that they can see, and that seems to make me more sure of it. They certainly don't challenge it. Reminder of what it looks like (not saying this would be appropriate in a suburban landscape!) It also keeps other dogs *out*, which invisible fencing wouldn't do.
We don't have too much problem with that since we're in a subdivison and you're required to keep your animals contained. Still there's a shepherd a couple of houses over and the owners walk him to the bus stop. Sam goes crazy when he's out. Watching him the other day run and literally choke himself on his collar (from the dog run) I realized he'd probably ignore the shock and keep going.
I've got some time. We've spent all our home improvement money this year. :-(