I had no opportunity to work with Laddie this morning, and temps were too hot for much work this afternoon. But when I had Laddie out in the yard, I saw an opportunity to work a little more on our devocalization training, though without an assistant and without a whistle. Also, I used the verbal cue "back" to send him from my side, but used silent casts for all our "over" casts.
First we did a repetition of our last session: no lining pole, bumpers thrown with Laddie watching to the pole's left and right, gradual increasing distances and changes of orientation within the bounds of our yard, and based on my discovery from yesterday, telegraphing each cast with a slight lean a second or two before each cast. We did a dozen or so of those and Laddie never vocalized.
Then I put Laddie in a sit in the garage, and went out to plant a bumper in each of the two places he had just picked one up, one on the right, one on the left, neither visible from any distance because of grass and rolling terrain.
I brought Laddie out and lined him up to run straight, to a point between the two hidden bumpers. Once he was lined up and locked in, I said "back". He leapt forward and barked, his first vocalization of the session.
I instantly called him back and gently lined him up, and then said again, softly but firmly, "back". He quietly ran straight ahead, until I called "sit", when he turned and sat, looking eager but not stressed. I leaned left, paused a moment, and cast him with my arm. He dashed to line's left, finally spotted the bumper, grabbed it and raced back with it. We repeated the sequence to pick up the bumper on the right, but this time Laddie took the first "back" cue without a sound.
I ended the session there. Laddie had only vocalized once during the session, and he had somehow made the one change on the retry needed to complete his retrieve, namely, not vocalizing. That seems important.
In addition, we had added a new element to the work: retrieving an article that he had not seen planted and could not see at the time of the casts. But this was in the context of a rehearsed path, so I would say it wasn't a true cold blind.