There are many feeders on the market for many different kinds of squirrels. Each one does an admirable job of keeping squirrels from monopolizing your yard. This is the key to understanding the function of a squirrel proof feeder. A properly designed feeder will stop squirrels from eating birdseed 95% of the time. There are no 100% squirrel proof feeders available. At some point, at some time, some squirrel is going to get some food. The feeder just shouldn't become a daily feeding station for them. Once you understand this, backyard bird feeding becomes a whole lot less stressful.
Keep in mind, squirrels are extremely territorial. The two or three you see in your backyard are actually keeping out the dozens that want to enter. Removing the dominant squirrels from your backyard, by any method, will only create a vacuum that will constantly be filled. I personally know of one customer who traps and moves his squirrels. He spray paints the tails to be sure they do not come back from where he drives them. After two years, he is up to 75 squirrels......and still counting! But, he is having fun, so we laugh about it.