I work from home now, but in my days in an office I adopted the following system - a small box on my desk with a green tick on one side and a red cross on the other. Green tick = I can be interrupted at any time, red cross = please interrupt me only for critical emergencies.
In both the old office and my home office I made / make a real effort to set the box to an appropriate value, i.e. don't have the red cross showing all the time or it loses it's meaning. These days it's only my wife who is looking to interrupt me, fortunately, but this system works well. And, hell, one of the benefits of working from home is having your wife 'insist' on taking you away from a 'red cross' task once in a while, heh-heh.
In both the old office and my home office I made / make a real effort to set the box to an appropriate value, i.e. don't have the red cross showing all the time or it loses it's meaning. These days it's only my wife who is looking to interrupt me, fortunately, but this system works well. And, hell, one of the benefits of working from home is having your wife 'insist' on taking you away from a 'red cross' task once in a while, heh-heh.