digging holes in the grass

Tsuki is a 7 month Maltese Bichon puppy. I’ve had her since 2 months. We live in a house with a medium-size garden. I can’t leave her alone in the garden for more than 10 minutes as she has the extremely annoying habit of digging holes in the grass. Holes around 6” in diameter and 6” deep. She gets chastised, obviously. I fill in the holes with fresh earth, which she will then, another day, either dig up again, or if I block access to that covered hole, she’ll dig another one.

I don’t think its due to boredom…she has toys to amuse herself, a tortoise to run rings round, and another dog to play with.

Any ideas on how to correct this behavior??????????? Its destroying my lawn.

Many thanks

We have friends who bought there dog a childs sandpit, place a few treats and toys in and the dog soon knows where he/she can dig.