Customizing the custom back button image usually does the trick.
self.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc]
initWithTitle:@""
style:UIBarButtonItemStylePlain
target:nil
action:nil];
As a third-party, I usually recommend that you do not violate built-in behaviors like this, especially since most iOS users are very familiar and comfortable with these gestures. Retrieving them simply serves to frustrate users.
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