Best way of preventing other programmers from calling -init

You can explicitly mark your init as being unavailable in your header file:

- (id) init __unavailable;

or:

- (id) init __attribute__((unavailable));

With the later syntax, you can even give a reason:

- (id) init __attribute__((unavailable("Must use initWithFoo: instead.")));

The compiler then issues an error (not a warning) if someone tries to call it.