can't nail (something) down

Unable to complete, do correctly, or be certain of some task or thing. I've been working on my speech for an hour, but I can't seem to nail it down. They couldn't nail down the terms of their agreement. I know I've heard this song before, but I can't quite nail it down.

Common Names:

Name	Pronounced	Usage
ÁIle	-	Sami
Ardghal	AHR-dahl	Irish
Chiarina	kee-ah-REE-nah	Italian
Kelvin	['kelvin]
Jolanda	yo-LAHN-dah (Dutch, Italian)	Dutch, Slovene, Croatian, Italian
Clovis	KLO-vis (English), klo-VEES (French)	Ancient Germanic (Latinized), French