Never, Ever, give your dog a command, unless you can enforce it. This is so important. If your dog is loose, and you call him to come, and he doesn't, what now? You call and call. If you do this, you have just taught your dog that he doesn't HAVE TO COME, unless he wants. If you can't make him come back, and he chooses not to come, he learns that he has the option to come or not. Do your training before you let your dog loose. Don't give them the option to turn and run. And if they do, just wait for them to come back and reward them when they do. Do not punish them for coming back to you. Work on the COME command.