snrub,
Usually, muskrats do not frequent open, well mowed areas. They tend to ponds with brushy banks for cover. I'm surprised you found a muskrat hole there.
We have had several muskrats. The creek behind the dam is a place they frequent and can live relatively unmolested. They will come up the overflow pipe, forage around the pond edge, then go back to the creek. I have not had as much problem since I raised the pond level by putting a 90 degree elbow on the overflow pipe.
Not sure what the hole is at water level in my 1/20th acre forage pond. Have seen no rat nor their feeding (cutting grass and weeds off at waters edge) but the hole has me concerned.
