Dogs naturally focus where they expect their reward to appear. When rewards happen at source, the dog looks at source in anticipation of the reward appearing there. This helps the detection handler to easily identify the location of source (the highest concentration of target odor).
Movement is motivational. You do not need a ball launcher to train your dog. But you can power up your rewards by letting the dog chase moving rewards, such as a thrown ball, a piece of food, or a food stuffed ball.
Note: Ensure that you practice rewarding away from odor first. If your dog is scared by a surprising toy whizzing by his head, he may make a negative association with odor. If your dog does not enjoy thrown rewards, walk to source and deliver them there.