Most cats come when they want to or when they think you might feed them. We want and need Prince to come when he is called for safety's sake. I started by using his name to get his attention - "prrriiinnnccce" and reward with something tasty. He is very responsive to this and responds to his name in most circumstances. However, we use our pets' names all the time, not just when we want them to come to us. We needed something that unequivocally means 'come here now' and ideally something that can be heard from afar. I use Prince's name followed by 2 taps on an adjoining surface like the floor, a chair or even a car. We started by practicing in the house again and again before moving out into the garden - and Prince comes running!