Some breeds of dogs have been specifically bred to herd sheep for hundreds of years. A great many of today's modern breeds have some or a lot of that in them, because the first deliberately bred dogs were shepherd dogs. If you have one of those breeds, or a mix, the dog will instinctively try to herd. If the dog is not trained to herd they way you want it to, then it will herd any old way. If you don't want your dog to chase sheep, get a Shih-Tzu or some other poofy floofy breed, whose instincts have been watered down to eat, sleep, crap, bark at nothing and look cute. Other than that, you'll have to take an active role in training your dog (probably should have before now), which won't be an overnight miracle. It takes a lot of time, diligence, patience, and attention to develop communication with a dog. If the dog knows what you want, he will do it. If not, don't blame the dog.
Just putting the cat near the dog, except put something between then like, putting the cat in a cat cage and the dog near it. Until they get better with each other and the dog wont chase it. If its a wild cat or just a cat that come in your yard, there's really nothing you can do, just keep the dog away.
Keep the dog on a leash. Perhaps a fenced in yard and some obedience classes.
The cast of Chasing Sheep - 2004 includes: Chloe Angharad as Vera Rhys Meredith as Dafydd
Keep them on a leash. Seriously, you're trying to work against dog nature on this one, it's hunting the cars.
Try to get your dog away from the other dog chasing it OR try shooing away the dog chasing your dog OR they might just be playing "chase"
A sheep dog.
Sheep dog
a sheep dog
Put the dog on a lead whilst passing chickens and every time your dog tries to go them pull back on the lead and use a Stern "NO"
Chasing the cat.
put him in a bench. Either tether the dog or lock the dog up in a pen.
Not unless the dog is changing speeds. If the dog is chasing the cat at a constant speed it is not an example of acceleration.