Now stay-forever is a much harder command to teach IMHO, even with the clicker. As soon as I started to wander away my dog would bolt and it took agility classes to finally get Gossy to stay as I walked away. Maybe because she knew she would have fun shortly if she stayed.
I think it makes it easier if there is an obvious high value reward coming at the end of the exercise. Not food, necessarily. "Do what I want, then you will get to do what you want" is a great incentive! "Forever" can be a hard one, however, and I don't think many dogs in practice are going to achieve this. I came closest with my Border Collie, who performed a (completely accidental on my part) two hour stay. Somehow I just can't see a Basenji doing that!!:)