Yes. One fundamental of of training is to be consistent without being predictable.
This sounds very simple (and it is) but that doesn't mean it's easy.
Right now your dog knows just what is coming up; a cast onto a retrieve. It's time to break that connection in his mind and introduce a degree of uncertainty.Currently you are doing the right thing, but not taking it far enough IMO. When you set the drill up, just call him in to you off the pitchers mound and do something utterly unrelated to retrieving. Heel work, sit / stay, lie down, whatever. Only when you've gone through those routines should you sometimes send him; perhaps one in four times(?).
You need to break the link that says "this is what we are going to do" and change the dogs expectation into "now pay attention; do just what I tell you".
Eug
