There are a number of squirrel repellents available (including fior ground squirrels) - googling brings up a number of choices, including coyote or fox urine and cayenne, white, black and chili pepper. If one or more work, any risk of pets or other unintended victims turning into rocks or getting poisoned is eliminated.
I have had gray squirrels cause all manner of work for me (chewed wires, taking up residence in my outbuilding along with the mess that created etc. ) but I'm not really upset with them. I have seen them do really heroic acts to save their babies from harm and I have seen them hug each other in friendship and I have laughed at their play. No hard feelings.
However, in empathy with those of you dealing with holes in the ground, I just found that something created an enormous hole near my house foundation - didn't see it sooner because it's camoflaged behind overgrown plants. I am assuming groundhogs but I have seen not a one on the property so I'm very mystified.
I read that groundhogs hate castor oil but that it won't harm them or others so I bought some today to try after I research a bit more about it....
JJ