Ps beware of the "back chaining" dog.
Ie the one that knows "sit" perfectly well but also has figured out that if she's deaf the first time you say it, and then eventually does a good job, she's more likely to get a good treat (oops).
PPS - you might find your dog learns hand signals more reliably than verbal ones. A lot of dogs especially the motion sensitive ones like herding dogs will. And also dogs that are a bit deaf (some herding breeds are prone to deafness).