Squirrel trapping is the most effective way of eliminating your problem, the traps are readily available about �15 each and squirrells are very easy to catch. place trap near trees with some fruit inside the trap. You need to deal with the trapped squirell with a few hours of it being trapped for humane reasons, you are not legally permitted to release the squirrell once it is trapped, it should really be killed, but I have released hundreds but always many miles from where they were caught.
good luck!!