The best way to practice distance
Once you have your basic send to obstacles (see 30-30 game), the best way to practice distance handling is to do it! Take any course and figure out how to use your real-estate (see article about that) to communicate the path. This is a sort of typical AKC excellent course that I am handling from the edge of the arena closest to the camera.
The only skills you really need are independent obstacle performance and the basics of communicating the path (see that article).
Notice that, I am still moving naturally and not artificially balancing along some taped line in the dirt. In other words, I am handling as-if I was constrained by a line, but that line does not take priority over the information I am giving my dog. This is key to building the confidence that you see Echo has in driving through this course.