Tonight, we worked more with the whistle and doing whistle recalls. I wanted to work more at distance to get him used to it. I also wanted to start letting the whistle be the only signal as much as possible, though I know I'll still need to help him with the meaning using one of already known cues.
Even with that, though, I made a change.
To play the game, we went to the black top in the neighborhood field/playground, and started I would go from corner to corner, calling him with the whistle. He had to come to front, sit, stay put while I went to the next corner, and then call him again with the whistle.
At first, I let him get all his 'business' done so that wouldn't be pressing on his mind. Then I went into some 'warm up' with the whistle recall at short distances. Gave him a little sniffing break and then played the game.
Did another short warm up again and then went into it. For the first round, I used a snap of my fingers as I did the third tweet (the whistle call is three short tweets). I praised him and went to the next corner. Kept this up for a couple trips around the black top, then gave him another break to walk around and such.
When time for the second round, this time it was just the whistle. I would do nothing else. This was sort of like a "quiz". I would give the whistles and that's it. He had to remember what to do. When he started coming to me, I would praise and encourage him (to start), and then that stopped. Soon, the game went like this: I go to corner, give the whistle, he comes front and sits, I praise and move to the next corner. The only sounds I made were the whistle and the 'good boy' (which he knows as much as a verbal reward marker as much as just praise - kinda rolled up in one I suppose). It let's him know he's doing it right, so he gets feedback while keeping him in a focused frame of mind.
After a few trips around the black top, I ended the session and had some play time with him. He did pretty well, and I think we both felt like we made progress. And, of course, we both enjoyed the play time! :)
Given how it went this time, I think we'll keep playing this game. It's like a variation of the "Station-to-Station" game we played to work on "go around", and it seems we might be on our way to similar success with the "Four Corners" game.