I had the same problem of squirrels in the attic, with holes that they chewed in the soffit for getting in and out. I bought some fox urine,which also came with small vials, and I nailed the vials up at each of the soffit holes on the outside. The squirrels left, since that had the smell of their predator. Then I closed up the holes, and they never returned. I got the urine at this website (of course, this poses the question of where did they get the urine?):
http://www.predatorpee.com/Merchant2...tegory_Code=FU
Good luck.