>I make a point of adding a permanent "Out of Office" block of time in the afternoon on those days.

Yeah, I have 3-5pm (our standard hours are 9-5) and a 1 hour slot for lunch in the middle of the day set as OoO every day.

>Outlook/Exchange has an option for your calendar to "Always decline meeting requests which overlap with others".

Wasn't aware of this, but yeah would only really be useful if I could set it for specific meetings as often the meetings getting out ontop of others outrank the first meeting - so wouldn't work too well as a blanked rule for me.