Entering South Africa on EXPIRED SA passport (as a dual passport holder(AUS/SA))

Question

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?

1. Enter on AUS passport and hope they dont notice his place of birth 'Cape Town'

or

2. Enter on expired SA passport and just tell them he made a mistake by not checking it early enough to renew for this trip?