Another thing you might try is offering only safflower seeds and thistle seeds (not mixed together, of course; I'm talking one kind per feeder), neither of which squirrels are much interested in, at least in my experience. Generally speaking *most* birds that like the usual sunflower/millet/etc. mix will also eat safflower-only, though apparently it is a bit of an "acquired" taste (they're quite bitter) and you may see visiting levels drop for a few days, after which they decide "Oh well, this'll do I guess" and come back in force. I've yet to find a "squirrel-proof" feeder that actually delivers on its promise; we just use ordinary tube feeders, although squirrels will chew right through the plastic on those if there's a kind of seed they like inside. I've never found a really good squirrel solution for suet cake, either--generally what we do is suspend it from a pole which we then grease with vegetable oil every few days, so that the squirrel slips if he tries to climb up. That's not a perfect strategy though because a few of them somehow manage to climb up anyway, plus also some squirrels are great jumpers and can rocket right up to the feeder from the ground.
Try asking the people at your Wildbirds, though--sometimes strategies that work well in one part of the country aren't the greatest in others, and chances are they're used to fielding that question from locals.