I really do think that there is something VERY wrong with using a shock collar to deliberately create a FEARFUL and avoidant response in a dog for performing an INNATE BEHAVIOUR (or any behaviour to be honest!)

Border Collies are herding dogs- over generations these dogs have been selectively bred for their ability to stalk, chase and herd! You are bound to see chasing behaviours in a border collie. What is important is knowing how to handle the behaviour by encouraging them to chase something that you DO want them to chase and thus satisfying their needs to chase. It is also important to teach them a chase recall, so that in a situation where the dog has the opportunity to chase something that would be dangerous, you can give your "chase recall command", say "TOY" and the dog will spin around for the object that you DO want them to chase. At the end of the proccess the dog will not even be taking any notice of the previous chase target. Obviously lots of training has to go on before this stage, such as performing the chase recall away from an identical toy and building up their exposure to the original chase target. Constant repetitions of playing with the "special toy" will mean that the neural connections in their brain between certain objects and "chase" will have changed. Hopefully you are at the point when you can compete with the original stimulus because the dog WILL ACTIVELY choose the desirable chase object.

Apart from anything else, collies can be very phobic dogs. Not uncommon at all in herding breeds. Training a collie using pain, aversive techniques etc such as shock collars will just create nervous and fearful responces

Please do not use a shock collar.
Contact a decent positive reinforcement based trainer, preferably with experience with collies who I'm sure will be very happy to help you.
This is a fairly common problem with collies so don't loose hope. What is so important in the short term is to play 100% safe, don't allow the dog to be offlead or in a position where he/she can chase cars or horses etc...

I hope this helped.

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