Never ever follow a dog that wont retrieve, all you are teaching it is to keep a safe distance from you when he has taken quarry, my bitch went a bit mad for awhile, she refused to hand deliver the bunnies to me, she would stay about ten yeards away from me and I soon learned that to ignore her, she did'en like been ignored and came in.
I would also try a wee bit a lure training again, this worked for me, a wee treat to start off with and then when you have him going strong on the lure cut back on the treats, worked for me.