Thanks Saddlebag. I have already studied and use the broader concept of Positive Reinforcement of which clicker is a part. A good primer for this is "Don't Shoot the Dog" by Karen Pryor, probably a book many horsemen would overlook because of the "Dog" in the title. It teaches you to train spouses and teenagers as well, and that would probably not go so well with a clicker . Karen was one of the early instigators of positive reinforcement training in sea mammals so is well qualified to write the book.
Whilst Parelli makes little use of PR it was interesting that at a David Lichman (David Lichman Licensed 5-Star Parelli Natural Horsemanship Instructor ) clinic he showed a video of PR in training a Sea Lion. He has trained with Jennifer Hurley Animal Training and Research International and listening to him talk about the parallels in training different animal species was very interesting.
I've used clicker extensively to help with Fillys' training, but have to be very selective as to when to give her treats. She has the horsenality of "hand over ALL the treats and no one gets hurt". But putting the behaviour on an intermittent reward schedule quickly works well with her.
As a progress update on the hind quarter yields, we did our first ridden sideways over a large traffic cone today. The tail still swishes a bit, but the eyes and expression are soft, so I am very happy with progress.
If I get time this week I'll start a thread on Positive and Negative reinforcement. That should get a pre-Christmas debate going