If this dog really was a "100%" leader, then I think he/she was probably not being challenged at all. Leaders, even great ones, make mistakes on things like 'Gee/Haw' fairly often and honestly, it isn't the measure of a leader in my team at all.
I'm often asked what exactly I think makes a great leader and folks seem really surprised when I say I don't care how well they are 'gee/haw' trained. For me a leader needs one thing - the desire to go. If you have that, everything else will fall into place in time.
Honestly, I mean that. When a good, driven dog wants to go and you are the one that controls if they go, it is in their interest to figure out what you want so they get what they want - to get moving again.
Of course, I'm talking about this now because I want to give an example. Today I went on a 26 mile run with 4 year old Tess and 2 year old Rocket in lead. Tess is an Iditarod finisher, so she has lots of experience running, but it is only this year that I have began to focus on her as a leader. Up till just recently I've been running Tess with seasoned leaders like Dasher, Jinx, and Sprite to build her confidence. The next step is to run her with inexperienced leaders to see if she will step up. Rocket has maybe 6 hookups in lead and is actually in her first season of serious training, so inexperienced she is.
The run went great. I stopped and held leaders when traffic passed just to be on the safe side, but both girls kept the team moving well, passed distractions like sheep, horses and loose dogs with only minimal issue, did great 'Gee Overs' (the first command I worry about with my leaders), and even got all their commands (although the trail wasn't particularly demanding in that respect).
But on the way home Tess did something that spoke volumes to me about the quality of leader she is to become.
We were passing a series of farms and young Rocket was quite interested in what was going on in each of the yards. She wasn't so much turning into them as drifting as she was gawking at dogs, people etc. As we approached the second driveway Tess ducked under the line and pulled out hard to the left (I don't neckline my leaders together). I commanded her to 'Gee Over' and she instantly swung to the right. That was odd I thought. As we approached the next driveway, she began to do the same. This time I didn't say anything and just watched to see what she would do. As I watched her swing wide again, it occurred to me exactly what she was doing - she was swinging wide and bracing herself to compensate for Rocket's drifting down driveways. Sure enough, as soon as we were by the driveway, she put herself back over on the right. The young lady has figured out the weakness of her rookie co-leader and is fixing things so everything continues to 'go well' on the run.
Now that to me is a leader!!!
Way to go Tess!!!
There are a few more pictures of the run at http://picasaweb.google.com/northwapiti/December262008