Is there a way to protect yourself against Naga Siren's ultimate?
Is there a way to prevent your hero from getting asleep from Song of the Siren?
BKB, Omniknight's Repel, Lifestealer's Rage, Juggernaught's Blade Fury, and the Earth Element of Brewmaster's ulti.
Edit: The first being obtainable on any Hero, the rest being situational as 'counter picks' against her.
According to the Dota2 wiki.
BKB (Black King Bar) is sure way of not being put to sleep
source:- http://www.dota2wiki.com/wiki/Naga_Siren