If you have an old clam shell you could provide him with a digging pit.
Just dump a pile of dirt or sand in there and put a toy or two or a chew in there and it might encourage him to dig there not the garden.
If you stash something in it every now and the it should keep him interested.


Get him a kong or two to keep him busy or whatever toy he's into.

A bone provides hours of chewy pleasure.

We put our dogs biscuits scattered on the patio so she forages for her food instead of scoffing it all from the bowl.

I saw a toy a while ago that hangs from a tree and drops a bit of food when they jump up to it - it looked like hours of fun.