This game is all about generalizing boundaries to everyday items you have in your house such as a towel, a box, etc. Once your dog has some household “boundaries” under their belt, take it out and about using real life boundaries such as a bench, a step, a tree stump, etc.
For dog-dog reactivity or dogs that have a difficult time maintaining calmness in changing environments, boundary baseball can be a game-changer. Be sure to play it on-leash as well as off-leash and play it between different environments such as a door leading from inside to outside or from your vehicle to a new area.