The antonyms for the phrase "going out of depth" are staying in control, maintaining stability, and standing firm. These terms suggest a sense of composure, balance, and security, which are the opposite of the feeling of losing control or sinking into unfamiliar and dangerous territory. When we "stay in control," we demonstrate the ability to manage our circumstances and maintain our confidence. Similarly, "maintaining stability" allows us to keep our footing and remain grounded in our situation. And when we "stand firm," we illustrate our resilience and fortitude in the face of challenge or difficulty. These antonyms represent the sense of control, safety, and reassurance that we all seek in uncertain or challenging circumstances.