When you provide free food for your birds, you are basically offering to any aspect of nature, including deer, fox, raccoons, and yes, squirrels. Learning to enjoy all of nature in it's glory simplies this hobby tremendously. Birds have learned to live with squirrels and a successful backyard birder can too.
Many of our customers use a humane trap and drive great distances to release these intruders into the wilds. We have one man who has trapped over 75 squirrels in the past two years and is still going strong. Oh well, it keeps him busy and he is having fun doing it. However, for most of us, living with a couple of squirrels is part of nature and we enjoy that as well.
There are a number of excellent feeders designed specifically to keep red, grey, and fox squirrels from monopolizing the bird seed. Each one can satisfy your desire to allow the birds to feed, but not the squirrels.