I have my 4th golden here. He is dumb as a rock..
.........when he wants to be
That’s not dumb; that’s rebellion. Very clever rebellion.
I assume you’re familiar with the Golden Retriever creep. You put one on a down & stay, and over the course of time, he creeps farther and farther away from where you put him, a little at a time.
He seems to know when your attention is not on him.