Best way to catch a ground squirrel is like this-
Get a gallon milk jug and fill it with water. When you see that little POS run in his hole, turn that milk jug full of water upside down into the hole. That little turd will swim up and out to prevent from drowning himself. He will end up inside that jug when the water runs out. Then you can have your way with him.
As for the muskrats.... Get you some of them poison smoke bombs from the hardware store. Fire a few in their holes over on the bank. Lose the .22 and get a shotgun with some 7 1/2. When they come rolling out let the 12 gauge blaze!