This question already has an answer here:
My husband is travelling back to SA in 3 weeks. He is a dual citizen AUS/SA. His SA passport is expired. What should he do when crossing immigration controls in South Africa?
- Enter on AUS passport and hope they dont notice his place of birth 'Cape Town'
- Enter on expired SA passport and just tell them he made a mistake by not checking it early enough to renew for this trip?