I have/had 5 thistle plants, this spring 2 of them suddenly stopped growing and one died, the other is making a tentative comeback... I dug up the dead one to see if I could find anything obviously wrong with it and part of the root was destroyed and there was a perfectly round hole slightly smaller than a US half dollar next to it. I dug up the hole a couple feet to see if I could find the creature but I didn't see anything... The creature has re-tunneled and has made a new entrance/exit hole. What kind of animal would do this and is there some way to make my garden less appealing to whatever it is?