strong and unshakeable
unwavering - firm
Something ‘unwavering’ will not weaken or subside and continues in a firm and steady way. The word is most commonly used in relation to a belief, position, or attitude. Unlike some of its synonyms, it implies a high degree of mental determination and courage rather than sheer stubbornness. For that reason, it has only positive connotations.
I couldn’t have got my business off the ground without my family’s unwavering support. They stuck by me through thick and thin.
Despite threats against her life, the journalist was unwaveringly committed to exposing the activities of the organized crime group.
It doesn’t matter what anybody else says, Helen is unwavering in her belief that this method is the best way forward.