Pesky squirrels... mines the same Mally. my twisted hazel is full of nuts and there in lies the problem ! We have 3 or 4 that use our garden on a daily basis for burying their winter store :o(
What is currently making holes in my grass is squirrels, every morning lately, I look out of the window and watch them busily bringing in acorns and chestnuts from the nearby woods.
When the chill of winter comes, I expect I'll be watching them again, running around trying to find where the heck they buried them.
I've got a similar problem with squirrels recovering nuts they have buried earlier in the year - the grass is scraped away in a circular pattern about six inches across.