Have the door closed during certain hours (slack has a dnd mode, which can be overridden if it is important) then people will learn to contact you during those times, especially if you down prioritise those who accept the system.
You are going to catch some slack, offset that by producing more/better than anyone.
What I haven't figured out how to do is do the same thing with work communications (Slack et all). Since I work remotely, it's important that I have a virtual office door that people can knock at. The problem is that if you too often have your door closed on Slack, people complain that you're never available. If you have your door open too often (the default), you always have this nagging feeling that you're going to be interrupted soon, so you may as well not start on anything that requires focus.
^^^ Does anyone here work remotely and have a good solution for this?