The demon could not escape.
"The fall of Communism opened a Pandora's box, from which all demons escaped, among them anti-Semitism."
"The demon has changed himself into a little monkey and escaped," cried a warrior.
A genuinely bound demon would have escaped, so I am free to go.
A spell was used on each portal to seal it forever, ensuring that the demons could never escape again.
And she knew they would be hunted down and rent to pieces if a single demon escaped her duty.
The demon would escape, to sicken other people.
The black smoke drifted among them, curling around their spiked crimson armor, like demons newly escaped from Hell.
It's the one thing that will stop you, because when invoked, it puts whatever it is aimed at within, and even a demon can't escape.
The blind priest is the guardian who ensures that the demons do not escape.