Unfortunately, this also makes them flight risks. When let loose (either by accident or design), they immediately bolt for the neighbor's yard across the street, and then next door, and then back the other way. On a couple of occasions, it has taken a LONG time to get them to come back (much to the chagrin of some of our house/dog sitters).
However, I feel guilty not giving them the opportunity to really stretch their legs. I also want to be able to play out in the yard with them without worrying about them bothering someone else or getting hit by a car. The electric border idea is one that we have discussed but dismissed for a number of reasons.
So, I've started loading my pocket with treats and letting them out. While they still tend to bolt down the drive initially, they have been coming back more quickly and have been much more responsive to my calls. I'm hoping that this will continue to work and improve their behavior while outside.
They've certainly enjoyed the freedom.