I just wanted to add what I have learnt with my two - the extreme car chaser and the wildlife chaser. Deska's is a herding instinct - he wants to stop people (his sheep) moving away from him, but isn't interested in chasing other things. Tully on the other hand loves to run and chase anything. I really think it makes a huge difference in dealing with the chasing knowing the reason behind it.
You all may remember how much I lamented about Deska's car and bike chasing, which the vet-behaviourist said was incurable. And I agree that even when I think he is getting better I can never let my guard down because he will never be completely cured. But we have made huge progress with cars (not so much bikes).
So now I make a really big deal of Deska chasing flocks of birds. We go looking for flocks together and then I rev him and and shout "go, go, go" when its time to chase. What it means is he now looks to me first when he wants to chase something because I am part of the equation in following his instinct and getting that level of gratification. And this gives me the time to grab him and redirect him before he goes off after the car.
Tully I have found just wants the adrenalin rush of chasing something. So I always take a ball with me and can generally redirect her to the ball. Or I will help her find 'bunnies' to chase. Let me tell you the local roo population is breathing a sigh of relief. It doesn't always work - sometimes the two of them feed off each other.