They mention a couple others in the article as well:

Bells on collars work, as does switching cats on to a premium, high-protein food diet, and giving them mental stimulation by playing with them in the morning. “Changing the cat’s food can reduce the amount of wildlife they kill by over a third,” says McDonald. “And playing with your cat, more than a quarter. These are positive actions for the cat that also have a positive outcome on their behaviour.”

It depends on the cat. One of mine figured out her bell was noisy and broke it off every time.