I don't think you should be using anything like 'look here' or 'what's this'... If you are asking your dog do do something - recall, sit, whatever - then that command should be all that is required. If trained to the whistle, the dog should respond immediately to the whistle. No 'oy', look here necessary. If you are training a dog its attention should be on you. Running across a field to show it a piece of cheese in the hopes it will follow you is not effective as a training method. The dog shouldn't be allowed to do as it pleases when it chooses. Insist on the correct response at all times, reward with praise or treats or a game once it has done it correctly.