In this video, Michael Ellis explains different ways you can hold a tug while playing with your dog. Presenting the tug to your dog in a variety of different places depends on what behavior you are trying to reinforce.
I love this kind of background, not just because of its directed uses, but because it teaches a great deal about baseline "dog logic," how physical and distributed is their way of memory. 'This is what you wanted me to do the last thirty times, so...' In a way, without programmatic exceptions, they don't need to think.