A boundary you never enforce is just a suggestion with nice handwriting.

A limit only exists in practice. Stating it is the easy half, and the other half is what you do the first time somebody walks straight through it, since your response teaches everyone what the rule really is. Repeated exceptions quietly cancel the original announcement. People learn from the pattern, never from the statement.

Pick one limit you have declared and not kept, and decide now what happens the next time it is crossed. Make that consequence small enough that you will follow through. Consistency matters far more than severity here.