Set in stone

Set in stone ( ou “carved in stone”): diz-se de algo garantido, firme, que não popde ser mudado / garantir firmemente algo

“These are just a few suggestions – they're not set in stone.”

“Though nothing is set in stone, Apple's plan could fundamentally change the television business, as networks would be looking at a different kind of...”(www.newsweek.com / December 22, 2009)