In my yard, I use to have beautiful grey squirrels. They didn't seem
terribly destructive, other than they ate some of the Cherries, and
apricots in the next door neighbor's yard. However, in recent years,
the grey squirrels have been pretty much overrun by another species of
squirrels that are more brown, a little smaller, a little scragglier,
and definitely more destructive. I have caught them red-handed chewing
on the roof to my gazebo. I can go out there and yell at them, and
they just ignore me and keep chewing, unless I get a little more
agressive with them.

I really haven't seen too much that has brought their population down,
other than having a neighbor pop them with a pellet gun!

I suspect you might try some kind of a rodent brick, but if you have
pets, you'd likely need to be extremely careful.

Goood luck!. . .and if you have any luck, please let us know!

Myrl Jeffcoat
http://www.myrljeffcoat.com