I have three dogs -- one huge dog, two small dogs (a Schnauzer and a Chinese Crested). If and when the Schnauzer finds a way out of my backyard, he inevitably runs a mile's distance in less than twenty minutes; and the Chinese Crested will always follow him, because the Chinese Crested doesn't like being left out. It should also be noted that, in Houston, if an animal is ever alone on the street it will be hit by a car. (Thankfully, the Schnauzer's fairly intelligent, and keeps himself off the roads).
Anyway, a majority of the dog's escapes are caused because the gate to the backyard from the driveway is old and crusty, and is sometimes difficult to shut. As such, whenever I let my dogs into the backyard, I always always check to make sure that it's closed shut. And when I let them back in I make sure that it's closed shut. And when I leave my house, I make sure that I close it shut (and if I don't, I start getting anxious, and I'm always positive that when I return I'll find both my small dogs smeared across the street in front of my house).