There is one author, Milo Pearsall who wrote Dog Obedience Training suggested tying a stick to a short length of rope and hanging it from the dog’s collar to prevent the dog from chasing. The stick is supposed to hit the front legs when the dog starts chasing. I certainly would not recommend this technique. This book was written in 1958, so hopefully ideas have progressed. It just goes to show that you can’t listen to someone just because they wrote a book. My recommendation is don’t have the dog outside without you being with it and on a leash. If it does start to chase, redirect it’s behavior with a higher profile activity. Pull out its favorite toy and redirect its attention until whatever it wanted to chase is gone.