never had to teach any of mine to retrieve as they have all been naturals until Wallace. Started at 8 weeks with him using clicker training for him picking up items at my feet then having him place them into an open hand, gradually put some distance on it, then took it into different environments.
All was going well to a point then he decided he would go and get the item then sit and play with it, I found that by me turning and walking away and having another of the same item he would then start to come back.
i also found he wasn't really fussed by food, and his ultimate reward is the throw of the other toy or dummy when he brings the first one back, which he only gets now and again, but often enough to keep him gambling.
really coming on now so progressing to doing directional retrieves with him.