Try it out on your free dummy site:

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Login Secure is an easy-to-use and user-friendly WordPress plugin that secures your website from unauthorized users. Blocks default WordPress login URLs and require a special code in WordPress Login URL.

After installing and activating the plugin, go to ‘Settings>>Login Secure’ link. Enter a unique string and click save changes.
Your WordPress login URL will be the one displayed on that page.

After storing a unique string, your default WordPress login URL will not work, even user can not log in by going to
http://example.com/wp-admin where example.com is your WordPress installation link.