Just work Wednesdays
Some companies also call them "No Meeting Tuesdays" which basically means that there is zero chance of a meeting being called for in the company boardroom.
This simple policy lets everyone know that the day is purely dedicated to work which means that they don't have to worry about any distractions. Why Wednesday? Any day could work, but Wednesday is the optimum day because it is smack in the middle of the week when the employees are best primed for work.