Whatever problem you're having with your dog, you should be able to cure it
Think carefully about the problem - why the dog's doing it and how you can change the training routine to correct it. Sometimes the dog will simply be using its own initiative to try to help you.
For instance, if he knows the sheep prefer to head for one side of the field every time they're in a certain position (maybe towards cover of some kind, or towards sheep in another field) he might well be staying out on that side to head or "balance" them back towards you.
Once your dog reaches the stage where you can trust him to work on his own for a few moments, try sending him out to the sheep and then just watch - let the dog do as it likes (within reason) and you may be surprised how well it works without you.