I'd take you're own ball to keep his attention on you.

We don't continue to play with Rupert until he drops the ball as he just won't let go. He's finally catching on after a long time but he's the same, if he sees another ball, he'll have it, his or not! Luckily he knows "what's this?" when showing him a treat/ ball which usually gets his attention in time!

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mummy to:
Kittes: Bella & Theo - 4 year old moggies
Doggy: Rupert - 2 1/2 year old Collie x
Chinchilla: Gypsy - Ebony