I've just experimented with the idea in post #5, but to prevent squirrels from scoffing all the food on our bird table. The birds can still peck up the seeds but the squirrels can't get their mouths around them, although they try hard enough.
Rats and squirrels go for my bird and hedgehog food
Margarine or any oil on the pole to the bird feeders keeps them off and the magpies
Both rats and squirrels hate chilli , curry powder, garlic , peppermint and lemon juice so the whole garden gets a blast once a week, twice in the winter