Polycarbonate/ plastic sheets (Hitchin SG4)

Hi. The squirrels in my garden have developed a taste for figs and almost everyone now is nibbled! I want to attach a smooth surface to the fence that they use as a runway to the tree to try to reduce access. Does anyone have any clear plastic sheets or something else that I can nail along the top of the fence close to the tree please? Open to ideas if anyone has had a similar problem