How can I safely remove a variable in iOS?

Question

I will use keychain data in various cryptographic operations and want me to delete any trace in memory after completion.

I want to prevent any memory dump or other low-level exploration that could expose a secret (or its derivative)

This question has a good description of what I'm looking for, however I am looking for an Objective-C approach.

Would it be a good safe programming practice to overwrite a “sensitive” variable before deleting it?