Squirrel proof?

We have had a long wait for the new bird feeder, around six weeks due to circumstances?
Anyway it has finally arrived and Rob filled it with sunflower hearts and peanuts, two of the squirrels favourite foods. We have an absolute plague of baby squirrels at the moment and they have been tucking in at an alarming and expensive rate!
The squirrels soon arrived for their breakfast and investigated. They were puzzled by the shiny sloping top and one fell off! The other one had a go reaching from the trellis but the narrow feed hole defeated it. After a while they withdrew licking their injuries and planning a new strategy for tomorrow!