Summit dog backpack training. Initially with an empty backpack. At 01:07 in the video he reacts perfectly naturally whilst wearing it and takes a shit without issue.
Maybe he's just tolerant... my grandson sits on him and he doesn't bat an eyelid. Follows him everywhere and sits near him whilst he plays with his toys. Herding / guarding instinct no doubt. You'd think he'd know better being 19.
Just kidding, he's 3. I get him to command the dog, so he knows his place. He complies without hesitation. I'm happy for that.
I took him out a few hours after the second video (so 3rd time wearing it) and he was chuffed to put it on, tail wagging. It didn't take him long to make that association. Although, he hasn't been out for a few days due to his op. I've put some little flashing lights on each side. He's jet black and almost invisible in the dark.