Marching to cannon mouth is a phrase that describes a dangerous or risky situation where someone is willingly putting themselves in harm's way. If you are looking for synonyms for this phrase, you might consider using words such as "courting danger" or "playing with fire." Other similar expressions include "living on the edge," "tempting fate," or "running a gauntlet." These phrases all convey the sense of danger and risk that is inherent in marching to cannon mouth. Whether you are describing a physical risk or a more metaphorical one, these synonyms can help you communicate the potential danger of a situation to your readers or listeners.