Although Chet knows Lexi and has played with her a few times. If she comes running up, or is passing with either one on leash he goes into a mode where he either doesn't take long enough to realize it's her, or is in such a state he can't recognize her.
Since he is the same way with her on leash have had my wife walking Lexi in a heel past Chet while he is in a sit and using leash resistance.
Has worked fairly well. After a day of this I walked chet in a heel while she walked Lexi. Chet did much better even passing dog side to dog side. Telling him what a good boy he was every-time we passed and he looked at my leg instead of her. On the closest pass of 3 feet he did make one quick snip towards Lexi after passing. Was expecting it so side stepped and changed directions, with a verbal correction. Made another pass at a further distance so we could end on a good note.
Repeated it again today with much better success. He even maintained a heel when I stopped beside Lexi and reached to pet her. No lunges even walking past with dogs on same side.
Between walks, for greater endurance, I would play a game of tug with Chet, pause and let my wife play a game with Lexi between walks.
During one session of tug with him a pack of dogs showed up at our fence barking and raising cane. Chet really impressed me. He was in a heel, when this took place, and even with all the commotion, and as much as he wanted to go after them, he never pulled on the leash.
During all the commotion, having heard of his propensity to redirect bite. I got him into a sit and used it to add leash resistance. After this I was able to get him to go into a down using pumps on the leash (flat collar), even as riled as he was, and maintain it within feet of the fence while I picked up something to run the dogs off.
Even though I was only able to get him to engage with the tug for a few moments after all this, instead of the normal game we usually have, as he didn't like his back to the area they had come from, All in all I am pleased with the outcome.