I have a large squirell population as I have a bird feeding/migration center set up...I don't even try to keep the squirells away..they can problem solve anything..
They ran through my seeded area a bit, they dug their tiny holes to hide their xtra food in and they only stole the sunflower seed, leaving everything else alone...
I provide enough food so no need to steal the one's I planted..but it will probably be different for you...

good luck...

Any chance of starting the seeds in pots? I've given up direct-sowing anything other than cornflowers and annual poppies and alyssym, because the germination rate is so awful by comparison with pot-sown plants. Between birds, squirrels, cold snaps, too much or too little water, direct-sown seed gets me about 10% of what I get sowing into pots. Even sowing outdoors in pots works better than direct, in my book - gives you much more control.