Training Disc Dogs

So I have a 8 mo. Catahoula named Ponyboy who likes golf more than I do. I've seen and heard of dogs that will dive into water after discs, and I was wondering what kind of training regimen I should start working on to get my "doubles partner" to start pulling his weight. He fetches rollers really well, but I'm not sure how to get from there to diving underwater to go get all the plastic I throw in N. Lake. Any disc dog training tips?