One Rear Toe On
The desired wait-for-release position of the dog is two front paws on the ground; two rear paws on the contact with the dog’s top line as level as possible. Having only one rear toe on is acceptable, but not the ideal. Although this position looks similar to “two on, two off”, the training concept for each is quite different (Two on two off is a front paw behavior and one rear toe on is a rear paw behavior). To help distinguish the two, the one rear toe on name was chosen.
The training methodology in the Clean Run article is correct and should result in a reliable contact behavior. However it has been observed that some dogs will not control their descent, going straight to the ground with all four feet and then stepping back onto the contact with a rear paw. This can result in a fault in some venues.
To avoid this behavior, remember to aim for the desired wait-for-release position. If the dog descends the plank intending to pause in this position rather than a stand on the ground he will work to control his momentum. In addition, do not spend much time at Step 3 where the dog is lured off and rewarded for stepping back. This step is intended to make the dog aware that contact with the plank with a rear foot is the important part of the behavior. As soon as he gets the concept, continue to progress through the steps.