Is it possible to make example.herokuapp.com unable to enter unless by certain dns?

Currently I make a dns that route from my website (example.com) to herokuapp (e.g. example.herokuapp.com). Soon, I will need to add the meta tags and everything to let google crawl my web. However, if the example.herokuapp.com would be the same as my current domain, which will make it also on google search. Is it possible to let the herokuapp.com to be able to access only via my website? P.S. Currently I am using Ruby On Rails to make my web applications