What is the best and secured way to implement admin page in a website?

Please read the whole question before saying duplicate.There are similar but this is different.

I have a website that users can post ads. Its written by using ASP.NET. So If a user post an ad it should go through a review path.( Involving an admin )

eg: User posting an ad. Then admin log to his admin page and review the ad and then give the approve.

I developed it within the same solution file. Currently I put this page in a folder. To access it user have to type

http://ift.tt/1J5BYen

manually. Please not that whole site is secured with SSL. Because that page is not linked from the main website. And this admin user doesn't have a user account in user account table.

So admin has to enter a password to enter this page. This password is hard coded( Not getting from the DB ).

So am I using the right approach? Can a hacker attack to this page?

I dont want search engines to index this page. Also what about this hard coded password method? Is it a secure way? Is it a good way to implement this page in this domain? I have different domains for this website end with .org and .info etc... Can I use such to access my admin page?

Tell me the best and secured approach to do this. Thank you very much.