at the last resort. In my region, the squirrels are definately protected in the city, strange as it seems. Exterminaters in my area will only trap the guys and haul them off somewhere else. So if you reside to a pellet gun or a CB cap, make sure that your neighbors or others do not see you.
I have had great luck with the following. My neighbor has three large pecan trees that hold a family of more than 12 fox squirrels. I hear them jumping from tree to my roof all the time, but do not have them in my attic. I have eave vents and hung tight wire mesh over them and on one side which holds the trees, I have an owl with a rotating head. Then at one area where they were digging around in the wood, I sprayed that area with fresh Red Fox Urine. Being a bow hunter I use this in my stand. It will really work for you, but it will fade away after a rain.