Vary the reinforcement
When your dog is learning a new exercise, reward every successful attempt for the best results. Once the exercise is known however it is not only not necessary to reward every attempt but this could prove harmful.
As soon as the dog is consistently performing the exercise correctly you should move to a varied schedule of reinforcement, rewarding every other successful attempt. Then move to every third attempt before going to a random schedule of reinforcement. You can also alter the value of reinforcements too. Give a ball for an average effort but reward extra good efforts with a tugger etc.
Nobody gets addicted to going to the cash point machine because the outcome is so predictable. We are aiming to get the dog hungry to do more in an attempt to win that big prize, just like at the roulette wheel. It is this exact process that leads to addictive behaviours.
Is your dog addicted to work?