Marking boundaries is an essential concept in various domains of life, such as personal, professional, and social. It is about establishing limits and indicating where one's authority begins and ends. Here are a few synonyms that could be used instead of "mark boundaries". The phrase "draw a line in the sand" indicates a firm stance on a particular issue. "Establishing limits or boundaries" suggests a predefined set of rules that should be followed. "Defining one's territory" refers to the protection of one's domain. "Staking a claim" is a more aggressive way of indicating boundaries, and "setting parameters" implies a system for determining limitations. Using these terms, the idea of marking boundaries can be better expressed and help communicate more effectively.