Another way which allows you to keep the dog working tracks that are a little older, is to work an older track at the time and distance that you know the dog can do. A good trick to motivate a dog and still work a track that is older is to lay the track and let it age. When you go to work the track post the dog on one side of a vehicle. The quarry then runs around the vehicle and slips into the vehicle while the dog is still posted out of sight on the other side. The handler then runs the dog wide around the vehicle with lots of enthusiasm to the starting point of the track and starts the track.
Articles are another way of motivating a dog.
This works best with dogs that have been trained to aggress or play with a track related article. This will help pull the dog along the track and can be used for both age and distance. The article placement can be just after a tough aspect of the track as a bit of a reward for working past this tough spot. For police dogs you can also use aggression at the end of the track as a reward for finding the quarry. This will work on dogs who are strong attack dogs and weaker in tracking.