Not all dogs care for the full fledge came of 'fetch". Most at best will retreive it maybe a couple times but then loose interest.

I would bribe some dogs with treats.

Teach him the command "Get It" or "Fetch" This means to pick up whatever object you are refering to in his mouth. You don't even have to throw it in order for him to learn this part. Just put it like a couple feet away from you, tell your dog to get it, and call him back to you, while waving a small peice of a treat he really likes. Hopefully he will come back you.

Eventually you can work with throwing it and having him bring it back to you. And as he gets better, slowly decrease the amount of times you actually give him a treat for bringing it back. But always give him lots of praise when he does a good job!