Next comes the big step. Take the dog out where he can hunt wearing the long lead, but where you are reasonably sure there are no birds. Walk around just a bit holding on to the lead and call the dog a few times when he is not expecting it. Enforce the command and reward as always remembering to always release the dog with "ok" as you send him off to hunt in a new direction.
Then let go and let the dog make a short cast or two. When he comes near enough so that you can get ahold of that lead without making a big deal of it, call him in and see what happens. It is important at this point to have hold of the lead before you call him so the the enforcement is immediate should the dog fail to respond.
By now, our pupil should really be getting the idea that you are always in control and learning that he will hunt only where and when you say. By repeating these sessions several times a week by the time that pup 6 to 9 months old, you should be well on your way to incorporating this lesson into a full fledged "run".
When you have the dog out at this point, still dragging the long lead and he is hunting away from you,, at times this may mean jogging several hundred yards to run him down. But get ahold of that lead ASAP and let him know that you did not appreciate having to come get him. Use a sharp, snarly tone and call him in. When he comes, get down and welcome him in and praise and reward him as before. Obeying the command must always be rewarded no matter what you had to do get to the dog to make him obey.
For real hardhards who seem to be off in their own little world at times, I recommend actually running the dog down and tackling the dog and rolling him over, giving him a good shake or two to let him know that he must pay attention and obey or pay the price. Once you have shaken him up a bit, grab the lead and back off and call him, he will come rushing in now most likely. Give him a big dose of praise everytime he obeys even if you had to run a mile to catch him. I don't know how many times I have had to say "Good dog!" through clenched teeth! This seems to work wonders towards turning off that "convenient hearing" that can develop with some young dogs. I feel that this is much more effective than a shock collar in the long run. If the dog feels that if he does venture over that next hill after he has been called, he may very well run into the boss over there and find him in a very foul mood. Training in this manner makes the dog want to get back to you ASAP when called and get the praise and lovin', rather than risk a good dressing down. Remember to release the dog and step off smartly to continue hunting off in the direction of your choosing.
The basic thing is that the dog must learn that he has a choice; he must come when called and get some lovin' or you are going to appear at the end of that lead he is dragging and get in his face about it. If the dog truly sees you as pack leader, he will choose to come in everytime if you are consistent in enforcing it everytime. If you choose to let him get away with not coming in when called at times, you are, in fact, teaching him that your calling him does carry any weight.
Soon the dog should be hunting with you at all times, checking back in and turning with you as he hunts without alot of "hacking" on your part. Be sure to praise and reward when the dog comes in on his own, remembering to release him off to resume the hunt. Dog's get a big kick out of obeying commands and getting praise, on their own without being told. It is at this point that the dog is truly becoming your hunting partner.
In time you can switch to running him with the shorter lead attached to his collar and then to no lead at all. But, you still must enforce the command at all times if he chooses to ignore you. Remember, only give the command when you are sure he can hear you and is likely to respond and if he doesn't you must go get him even if you are hunting. It does no good to yell at a dog that is already a quarter mile off busting birds or chasing deer. If the young dog does here you at all at times like this, all of your yelling simply teaches him that it is more fun out where he his. Call the dog once, be sure he hears it and then go get him if he does not come in. In this way the dog will stayed "tuned in" to you and not learn to ignore your fuming and fussing at him.
This all does take time, but surely, with diligent application, by the time the dog is into it's second season, the two of you will surely be working as a team, hunting where you want him to hunt, under nearly perfect control as he strives to find birds for you to shoot for him instead of you hunting for him with him off looking for birds for himself.