slit seeding vs aerating...or both???

Hi all,
We are going to try once again to get some fescue to grow in our yard. We have a shady backyard, filled with thirsty oaks. Needless to say, it is hard to get anything to grow, with limited sun and moisture hogging tree roots. We are considering either renting an aerator, a slit seeder, or both...but for cost reasons would prefer to only rent one. We will buy a bag of fescue seed approved for our area. Will the slit seeder alone be more beneficial than the aerator? Our ground is very hard. Should I just aerate? Or should I make the investment and rent both?
TIA! Heidi Raleigh, NC
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