Squirrels are cute and everything, but can be a real nuisance. Especially when you're trying to feed just the birds. We had invested in a weight-sensitive seed feeder, and a cage for other seed feeders. We had been hanging a suet block feeder out at one of the ends of the bird feeder structure's arms. Recently we discovered a squirrel had found it.
So we had a number of options. We could increase the height of the post, and install a post baffle, but because the deck railing was 36" high, the baffle would have to be positioned at least 4-feet above that, making it very difficult for us to actually reach the feeders to refill them.
After doing a little research I decided to try 1/2" hardware cloth. I bought a yard of 24" wide hardware cloth (mesh) from the local hardware store. I cut and bent it to fit inside the suet feeder. It needed to be a tight fit so the suet blocks could still be inserted easily.
After about 20 minutes of cutting and bending, I finished. On testing, the squirrel tried several times but gave up after a few days. The mesh is large enough so the woodpeckers and other birds can dine to their heart's content.
Now entertaining our cats go a little less expensive!