That does not work for some people. They just don’t get it. They will open the door and walk right in. Doesn’t matter how many times you ask them to do otherwise.
I have this problem. I plan to try this trick myself. Sad that it’s necessary, but happy that this may be a solution.
I think being able to make such people understand is an important social skill. They obviously understand the meeting thing. Why is that? You need to react to every interruption in the same way you would if they interrupted a meeting. Allow yourself to be genuinely outraged that they would even think about crossing the threshold. It's OK to have boundaries.
I have this problem. I plan to try this trick myself. Sad that it’s necessary, but happy that this may be a solution.