I use Tom Chambers squirrel proof feeders - not cheap, but very effective... and I like the look of them.
Birds like to be able to see what might be coming at them from all angles, so consider that when you position your feeders.
If you put up bird boxes, you can buy discs to go over the hole, so that squirrels can't chew at the entrance and get in. I buy food in bulk bags and bulk fat balls from Ark Wildlife - they do the bird box hole covers, but you can buy donut shaped ones on eBay, which is what I've done.
Our nest box protection helps guard nests from the environment & provides wildlife with a sturdy home to rest in. View our range here.
www.arkwildlife.co.uk
The RSPB website is a good source of information and if you visit a local reserve you'll find people happy to answer every question you can think of. You can join the RSPB on a 'pay what you can afford' basis with direct debit. Membership gives you free entry to reserves and their car parks, and a monthly magazine (or it might be quarterly - can't remember how often I get mine).
Have fun.
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