We use to have the same problem, so I took empty plastic juice containers (the kind that Fruit Juicy Juice comes in, clear 64 oz containers) I take a knife and cut a slit along the length of the container, this allows me to sort of open it up and place it around the pole. I put three stacked one after the other up the pole from the ground. They can't jump that high so they can't grip the pole and they fall back down.
I have had these on the poles probably a good 5 years, good summer or winter. And it didn't cost anything.
Good Luck