it can be cured. As said if it doesnt come straight back turn lamp off. When the dog eventually comes back dont make fuss or even talk to the dog, just put lead straight on the dog. As you said he will come back at first so make a huge fuss of him even if you look daft and scare all the game away it doesnt matter. Also start him again with the dummy in the garden or even better a alley way so its back to basics but if the dog is good and you like him its worth trying. All the best