There will always be brute force attack on your WordPress site no matter how strong or reliable your admin password is.
One way to secure the admin page is by hiding the page from public access.
This can be achieved easily by changing its admin address that will be known only to you.
There are many free plugins available from WordPress that can help you to rename the admin URL, such as 'Rename wp-login.php', 'Loginizer', 'WPS Hide Login' and more.
Please refer to the steps below to rename WordPress admin URL.
1. Login to your WordPress admin site.
2. Under "Plugins", click Add New.
3. Search for ‘rename login’ in Add Plugins page.
4. Click Install Now to start installing the plugin.
5. Once installation is completed, click Activate to activate the plugin.
6. Edit the new admin URL and click Save Changes.
You may access your WordPress admin site using the new URL now.