It’s going to be very hard competing with such an amazing self-reward. Here’s what I did with Henry and squirrels. I had him on the lead (very important) and walked him towards a squirrel. As soon as he noticed it, but hadn’t already got excited, I turned 180, keeping Henry close to my leg, brightly saying one of his nicknames (Pen Pen) and as soon as he looked at me, I gave him the BEST food reward (for him, cheese or hotdog). Repeat at every opportunity.
Over a few weeks, we were able to get closer and closer to the squirrels and still be able to turn away. Now he just looks at squirrels and remembers how good NOT chasing them feels. I still reinforce occasionally, and.calling Pen Pen! is our cue to look away from distractions and to me.
You’ll have to keep him on the lead for the duration of this training, though.