I get the tops of the balls and sew them . I call it doing surgery. lol When Grandpuppy bites the stuffing of her toys which isn't too much., son puts it up and say we need to wait for Grammy to do surgery. Anything to keep that little girl happy. I use thin fishing line its stronger than thread. Of course you always need to do a check on their toys every so often to make sure they are not eating the stuffing as a snack. That's what works for her. I have had great success with it. And she sits on the floor and waits till Grammy is done sewing.
Also , wash the toys every so often , I put them in a pillowcase and tie it. Enjoy your weekend.
