Having the joy of walking with your dog(s) off leash is an exercise that takes some effort from you and your dog. The key is to build a trust in both parties, and this trust should connect you two.
Start with building a very close and trusting relationship with your dog and make your dog understand that you will be there at anytime and any situation.
Use a 4 0r 6 ft. leash and at first let your dog walk beside or behind you for 5 min. then loosen up the leash and let your dog to be free as much as it wants for few seconds. Then bring it back to your side. This is allowing you to correct your dog and communicate to your dog that you are in charge of the walk and it should be walking beside you. Repeat this few times.
After that let it walk beside you for 10 min. and then you will feel that even by loosening the leash your dog would just walk beside you for a while until it realizes that you are not really holding on the leash and it may start going further from you. Bring it back and do it again and again until you can have a walk that your dog will be beside you but not pulling you and on leash.
Now, after few days allow your dog to pass you but then call its name or make any sound to bring it back beside you. If it responds to your command then you are half way there, but if not then bring it back beside you after the name or the sound is called and walk on leash.
This will take some time and patients; so keep trying till you and your dog master it.
Remember, anything is possible.