The phrase "deep moat" refers to a protective barrier or advantage that makes it difficult for others to compete or overcome a certain situation, making you safer or stronger. Full definition
Why would these school superintendents lower the drawbridge while others are digging deeper moats to keep charters out? (educationnext.org)
However, they all have one or more of the following characteristics: a deep moat, an energetic leader, steady and growing cash flows, and multiple revenue streams. (cnbc.com)
As more houses were built, the walls were extended and a deep moat was dug so that all could feel safe. (bookbrowse.com)