This is the only way. Yes, a reputable company operating in a country that respects laws will respect your robots.txt or some sort of future no-ai tag. But everyone else won't.

captcha is a way too

Captchas will not last much longer.

Captcha does not mean a simple image recogniton. It is for recognizing a bot using other user interactions. Bot can create login easier than that.

Except if you are forcing people for giving a phone number for viewing a blog post , and want that china thing where if you not smile walking through a gate, your credits go down.

Edit: let be enough a third party service (namely a capcha, which uses my general "login") which assures a site that I am not a bot.