I have taken those same "Yorkie sized" tennis balls and stuck them into a knee high stocking. You tie a knot at the end where the ball is. Schatzie grabs the end of the stocking and flings it and it just bounces back like a boomerang (sp).
The shoelace sounds good too.
***Just a safety note**** Always supervise during play as any string / stocking / long enough rope type item can be a strangle/suffocation danger.
Just wanna keep our babies safe
I wanted to add some pic's to this post as I had a few questions asked about the type of sock and ball etc....