When my cocker was very young she started to get obsessed with balls. So I stopped bringing them on walks, I put them away for a few weeks. In the beginning she kept stealing other dogs tennisballs in the park

but she got better. She still loves tennis balls, footballs, basically anything round but she is not quite as obsessed with them.
I only throw smaller balls in the garden, and she has one big plastic ball we use inside as reward in training (she loves heading it back to me). Other than that we use other toys or sticks (I know I know it's bad, but I'm careful how I throw them). It was just too stressful to have her stealing balls, interrupting people playing football in the park

so I'm glad she got rid of the worst obsession.
We had one really funny experience. My puppie stole a ball from a german sheperd in the park. One of those massive rubber balls. And it was so big she could not get it out of her mouth. So instead of running away with it and hiding it as she used to, she came trotting over to me for help, looking defeated and embarrassed. Of course five seconds later she was happily chasing that very same ball
