I also feed birds and had a terrible time with the squirrels getting into the feeder and emptying it of food with most of it going to the ground. I had the problem until I hit on a simple solution. All I had to do was put my feeders on a shepherds crook hanger out in the yard far enough away from the trees, fence & house so the little buggers couldn't jump up on it from one of those platforms. I then put a metal squirrel guard on the pole of the shepherds crook high enough so they couldn't jump on it either. To make sure it stayed up there I put a screw type hose clamp under the squirrel guard. Problem solved.
But I didn't want the little beggars to starve so I put a corn feeder up in tree away from the bird feeder. The feeder has a screw on it that goes into the corn cob so they can't just run off with the whole cob.
It's interesting to watch one squirrel up on the feeder eating the germ out of one kernel after another and dropping what's left and then another squirrel eats the leavings. And then there are the squirrels that apparently don't like corn and would rather eat the sunflower seeds that the birds spill.