Become less predictable?
When I was training Oscar sometimes I used to hide from him, or if he was distracted, I'd turn and run in the opposite direction. It teaches them to watch you all of the time. I sometimes still try these methods but they never work anymore because no matter what hes interested in, hes always aware of where I am.
When I was training recall I would only allow Oscar so far away from me before I would call or whistle. And I did this constantly, so much so that he will only go so far before turning and coming back without me needing to call or whistle now, its ingrained (very useful for beating on shoots).
EVERY time he comes back to within about 6 ft of me I verbally praise him, convincing him that to be near me is a good place to be. Don't become too laid back, even if you have taught good recall, it constantly needs to be reinforced.
ps A whistle is very useful if your dog goes some distance away from you and bearing in mind dogs get de-sensitized to our voices, a whistle is usually more effective outside.
Good luck
