Boy, from what I've read, those who do the job of 'keeping the course moving' are kind of between that rock and hard spot. I have no real fixes, but here are some observations and my ideas:
1. Played on of the best courses in my area this fall. They have 10 minute starting time intervals. It was the slowest round I've played (5.5 hours) in YEARS! At what point do tee time intervals fix slow play? No answer here!
2. The groups who play from the tips are usually influenced by the one guy in the group who can break 80. The other guys are overmatched and slow down pace. Idea: Close the back tees on weekends/busy days or move them up to the BACK of the next closer tee boxes.
3. The MOST time I spend waiting during a round is caused by the group in front of me playing on and around the green like it's Sunday at the US Open. Idea: Establish a REASONABLE amount of time it should take to chip on, putt out, etc. Look for the US Open guys and time them. Share with them what is reasonable and how their group compared. This way, you have something tangible to share with a group playing at US Open pace while the course backs up.
4. This is a great idea I saw on a public course while playing on a Sunday afternoon: The course hired young kids, probably 14-16 years old as spotters on some holes where tee ball landing areas resulted in players spending time looking for balls. Much easier to hit that 2nd shot in a timely manner when someone has already FOUND your tee ball.
5. People show up LATE for their tee time. I liked the story about a professional golfer playing in his first Masters tournament. The official starter told him this tee time wasn't the 'show up on the tee box' time but it was the time for him to be teed off and GONE from the tee box. Penalizing late players by moving the NEXT group who is ready should provide an instant lesson: Show up late for your tee time at this course and you LOSE your tee time instantly! If the late group has an issue, offer them the next available tee time or refund their money.
Finally, there is no excuse for slow play other than ignorance. My wife has been playing for 5 years and regularly shoots 100-120 from the forward tees. Our usual pace is 3.30 - 3:45 for 18 holes. And that's a leisurely pace that includes my wife hitting several 'do-over' shots. If you can't complete a round in 4 hours, YOU are the problem!