A boundary you enforce once is a suggestion. One you enforce every time is a fact.

People do not learn your limits from the announcement, they learn from the exceptions. Hold it four times and let it slide on the fifth, and the fifth becomes the real rule, because that is the round that showed them what happens when they push. Nobody is plotting. Everybody runs on evidence.

Pick one limit and hold it exactly the same way for a month, including the day you do not feel like it and the day they have a genuinely good reason. Consistency does the work, not the wording. After a few rounds the testing stops, because there is nothing left to find out.