The best way to kill a dragon is to unspeak it. See, they are huge targets sure, but still good luck hitting a vital organ. They might as well be able to shift their hearts about for all we know about their insides. And anyway now, that is forgetting about their hide. Such a big animal needs a thick skin to hold together all it’s juices, but a dragon’s surface is more than naturally resistant to penetration. Come to think of it, the only weapon I have any record of piercing a dragon is one of the swords made from that meteorite thousands of years ago. That’s its own story but if you want a space rock weapon now you might as well get in a rocket and grab some star matter. Hmm? Drowning? Sure, if a dragon needed to breathe. Burial? Maybe, if they weren’t able to practically swim through the earth. Toss ‘em in a volcano? That's the spirit. But they do exhale fire, so...hmm? Ah, yes, unspeaking, well. The dragons each have a name. An ancient sound that was spoken once to bring them into our reality. Simply say their name, and the right negator, and hey presto! Well, yes, that’s precisely it. No one knows their names anymore, and the language of creation is almost entirely forgot.