If your squirrels are anything like mine it would have to be a glass bottle, preferably still hot from the kiln to even put them off slightly! Mine squeeze through the bars of an (allegedly) squirrel proof feeder. Fun walking down the garden and seeing them trying to wriggle out quickly though - bit of a Pooh in Rabbit's warren thing really.

But, back to the subject - these look great, and wouldn't need filling so often.

__________________
Nell