How to prevent page from indexing

The Client complained about issue, that have occured when website was tested using google search console. The issue is: google search bot is indexing some pages included in robots.txt. So it seems to be a good idea to put meta tag <meta name="robots" content="noindex"/> in head of pages to prevent indexing. But the website consists of php templates and I have very very basic understanding of php. So can I just put a meta tag inside a specific php template even if it would be not head, but body of document?