[Dixie]

Squirrels hate mothballs. Put some in old pantyhose, and then hang them in the attic near the edge of the roof. The smell will last a couple months. That may give you a reprieve.

Second, don't use rat poison. They'll wind up dead all right. But they'll be dead inside your wall.

The really answer is you need to find out how they're getting in and seal it. Call a professional if need be.