I realized that outdoor spaces are still too overstimulating for him. We need to get more success in busy indoor spaces. Yesterday I took Cai on a shopping trip to Home Depot. He walked with me all around the store as I picked up homesteading supplies. Then I packed my goods into the car, picked up my treats, and went back in for training.
I picked a quiet aisle and let him look around, and gave brief praise and petting when he looked at me. I think it was about 10 minutes in that he started to look bored of just watching and wanted to do something more interesting. I tried out asking him to do a few tricks just for attention and petting, which is medium value compared to treats, but he often accepts it as a reward (and it successfully increases behaviors) even when he's too overstimulated to eat. I did see an brief increase in focus and willingness to perform a sequence of behaviors. However it was not a pretty, enthusiastic performance. Then I pulled out the chicken, and he lit up and wanted to work.
We did one trick per reward at first, then combined them into sequences of up to 4 tricks, but none of them required sustained focus beyond heeling 2-3 steps. The rapid cues served to bridge better than doing one trick for a longer duration (such as a long stay or heeling farther).
We moved out of the quiet aisle and toward a corner at the front of the store. There was a moderate number of other shoppers. We did more short sequences of multiple tricks. Cai did better than I'd expected! He barely lost focus as people walked by.
I'm feeling proud - and even better, like I finally have a clear way of progressing toward my goal: a dog who will be able to focus in any environment, whether a trial or a busy public market.