The problem here is trying to establish his coming to you in the garden. He needs to establish first in much more confined conditions mostly in the house! If you try this in the garden it is obvious that he will win the battle as once out you have no control. Get other family members to call him for no reason at all in the house say from the kitchen to the lounge and give him a treat every time without fail when he comes and make a game of it. Rememer, do not shout, scold or slap if he does not respond, just real excitment, praise and kisses when he does. He will learn to come to you for the fun of it and for the reward of food and then when you really need him to come he will do it automatically without thinking and it will not be asssociated with end of play etc.