I do a lot of dog training. I have a German Shepherd Dog and a Rottweiler, both are Schutzhund III. They are both SAR dogs, although the Rotti is retired. The GSD does 4 miles with me a few times a week. Both the Rootie and GSD have perfect off leash obedience.
Go here
http://www.leerburg.com/forums/ubbthreads.php for some great tips.
Use the choke or prong collar, but use them correctly. Another option is an electronic collar for off leash work. I feel that a Halti or Gentle Leader do the dog a disservice.
A couple of quick tips. If the dog is just a little bit ahead of you, without saying a word, make a hard left turn. This should put your knee right into the dogs side. The dog will learn not to forge ahead and to stay in a position where he can see your knee. If the dog is well out in front of you, do a 180* turn. When the leash gets tight the choke collar will do its job. Don't miss a step, pull the dog like it's nothing and the dog will self correct. After a few hard corrections the dog will get the idea