Take a look at this thread- there are some really good ideas on here:
chasing cars!!!!

OK- just a few thoughts from this:

DO NOT USE A SHOCK COLLAR!!!! This is a cruel and barbaric way of conditioning a dog give a fearful avoidant response towards something. As a collie owner, I can tell you that fearful behaviour can often worsen chasing behaviour. When a dog chases something they get a massive dopamine (feel good hormone boost). They enjoy this and so actively seek out opportunties to chase as a result. If a dog experiences stress (through a shock collar/ fearful response as a result of it), they will often actively seek out opportunities to chase EVEN MORE in order to balance out the stress that they are experiencing.

First things first, you need to keep your dog onlead around the things he chases; cars, bikes, horses.
Collies have been breed over generations for their ability to chase and herd, so it is no surprise that your dog is doing this. You have to control the opportunities that he has to do this. Only let him off the lead in secure areas where you know that there will be no cars, etc...

Teach him a chase recall. This is the best thing to do with a dog that chases. Most dogs that have a chase instinct will always have a chase instinct, this is not something that you can train out of the dog. However what you can control is WHAT THEY CHASE. In my experience, collies tend to work on rails, i.e. if you can get them totally focussed on something you want them to chase, e.g an extra special toy.
The following piece of text is copied from David Ryan (ex. police dog trainer- who uses positive reinforcement)
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