Some dogs can be very stubborn on re-call, our Wolfhounds will do the same on occasions. We train our with home made liver treats, they will track you down a mile away for them, every time they come back, give them a treat with masses of praise. Never ever raise your voice or show your displeasure when they come back after a lot of calling, they only need to know about positive things when they return. Also search youtube for Dog re-call training, Im sure you will find lots of useful tips there.