David said: "That's a terrible idea."
David said, "That's a terrible idea."
"That's a terrible idea," David said.
"That," said David, "is a terrible idea."
"That's a terrible idea.
"For one thing, it would be really expensive.
"For a second thing, I would probably get killed."
The missing close-quotes tell your readers that the same person is still talking.
"David, why did you come home so late tonight?"
"Sarah, you're always nagging me!"
"David, it's not nagging! I'm worried about you!"
"Give me a break, Sarah!"
If you and your sweetie talk that way, don't come to me—go find a counsellor. But do keep the he said-she said expressions to an absolute minimum.