If there are certain sites you prefer to browse in secret, for example YouTube, you can automatically switch to private mode when you enter into YouTube, so that no one else knows what you are looking at. You can do that in Opera with an extension called AutoPrivateTab.

Install AutoPrivateTab from Opera add-on page. After installation, go to extension preferences page (Ctrl + Shift + E) and click AutoPrivateTab’s preferences box. Just enter the words to the watch out for, for example, youtube (case sensitive) and save the settings (see screenshot above for details). Now, when visiting a site, it recognizes web address that contain specific words and automatically opens them in private mode. Happy browsing!