I often hear my clients say that they are afraid to walk their dogs off leash in an un-fenced area. They fear that their dogs will run away. Mind you we live in an area with miles of beaches and trails that are open to unleashed dogs, basically dog heaven. Meanwhile, I walk these same dogs off leash very happily with a few caveats.
The biggest mistake people make with their dogs on walks is not walking far enough. Most dogs are energetic and adventurous, they can easily walk/run a mile or two. It should take you about 45 minutes to an hour to walk 2 miles at a reasonable pace, If your walk is too short for the energy level of your dog than the dog is likely to extend their walk on their own by disappearing for a while as you approach your car. If this occurs don't panic, just calmly wait near your car. The average time for a dog to disappear I have found over the years is 20 minutes. You will most likely catch a glimpse of your rebel nearby within that time.
Another strategy to counter act end of walk disappearing is to bring treats and stop and give your dogs treats when you are about half way back to your car and leash him then to prevent the dog from running off when they catch site of the car.
Another important strategy is to vary the locales of your walks. The more familiar a dog is with the locale, the more likely they are to go off from you to explore. As they feel confidant that they will be able to find you.
Dogs love to explore new places and run free, so skip the gym and get out there and walk your dogs!