Pepper in the bird feeder. Have you ever watched a squirrel sneeze? After a few
pepper experiences, the squirrels are not nearly as enthralled with the bird
feeder (or planters since my squirrels feel it is their duty to "unplant"
anything in a pot on my deck.)

A neighbor has rigged plexiglass plates on top posts of his feeders and below
the feeders. The squirrels jump on the plexiglass plate then slide off because
their weight tilts the plate downward. It's great fun to watch the squirrels
try to land and be balanced on these "plates."