One of the things I do to keep M/Z busy is to hide the treat ball inside/under a blanket. For Magnus, he's really good at it so I put the treat ball inside the blanket, tie a knot for him to undo. This also gives provides for any urges for digging.
Here's a video of both Magnus and Zoey.
https://www.youtube.com/watch?v=Kgp66S3oaYc
For Zoey, she's too small to undo the knots so I just need to put it under the blanket.
https://www.youtube.com/watch?v=5qVJ2Ax0QbI