Once Congo is exploring a new place or tired of doing what we ask, food is not a reward. We've used everything from bacon to steak to dog treats to kibble. Even if he happens to come when we call, he'll ignore the food and look at us with disdain. :p His primary motivation is movement.
One of the things I have noticed by reading this forum is that many people don't know how to do positive or "reward based" training very well. You are trying to condition the response, not feed the dog. Failure to move to an intermittent reward system can result in failure of the training to "stick". What keeps people at slot machines? Wondering if the next time will be the "payoff"! Works with dogs, too! And it isn't just about how salient the food is, although that helps with early training. Anything can become boring or "less desirable" than freedom as it becomes commonplace. There is more value in something that is rarely available, so if you want really yummy treats to have an impact, use them sparingly. (I believe this is the foundation for the "really reliable recall")
I would add, don't "wear out" the dog by picking at him all the time. If you are at a social gathering, it might make sense to give him a short run, then confine him while you socialize rather than letting him wander around and constantly having to call him back. Then when you have time to give him your undivided attention, give him another opportunity to enjoy his freedom, possibly as a reward for obeying a few commands before you release him. The worst thing you can do is allow him to think that obedience is "optional". It is just too easy to teach a dog he doesn't have to be bothered when he doesn't want to, even if that isn't your intent.
