My sound solution works! Yey!
The yelling is now much less frequent, and if he happens to forget and I "fall asleep", he quickly lies down on the floor, waiting patiently for me to "come back to life". It feels indescribably good to finally have found a solution to that problem!
Nina wrote an interesting piece on being more clear on what we want when shaping. She sort of summed up some of my thoughts around this, and it also related to this sound solution thing. Worth reading!