Slow play is a problem, and I too don't see any real solution other than doing what I can to educate the casual golfer I play with. If my group is having a problem keeping up, and I see any obvious issues with anyone's play, I will try to find a tactful way to broach the subject. I don't want to incite a fistfight, but in my experience, most players are quite receptive to reasonable suggestions. Other than that, find a course to play at where the rangers actually do the best that they can to keep things moving. My home course rarely has a significant gap between groups, but there are days when the afternoon rounds drag out to 5 hours... all it takes is several foursomes lagging a shot or even a half a shot behind the group ahead, and it adds up fast. Yet there isn't any real culprit for the ranger to identify and focus on.
I work as a starter, and we send groups out at 9 minute intervals. That is plenty of time for a foursome to play their 2nd shots and clear the fairway... the guys I play with generally have played their approaches to the green on the first hole in 5 or 6 minutes from the 1st player hitting his tee shot. The problem is that it only takes one player in a group getting into the weeds... and taking even 2 or 3 minutes to search before abandoning the ball as lost and playing his provisional (or as so many do, dropping a second ball
). If that happens on a couple of holes, the group is already playing catchup... and that's only if they acknowledge the fact that they are behind. Or if there is a ranger to inform them of the fact.
As starter I record the turn times for every foursome that comes through from the 9th green. They pass right in front of my booth, and I know when they started. If a group is too far out of position, I send someone from the golf shop out to inform them, and I call the ranger on the radio to let him know of the problem. He will hang in their area as encouragement until they close the gap, and counsel them further if need be.
I know that a lot of guys say that the rangers on their courses don't do their jobs, and I can't speak for them, but the places where I play regularly, all have pace of play policies, and all enforce them as far as reason will allow, but aside from an extreme case, you simply can't just evict a foursome from the course... not a public muni like I work at.
The players just have to accept that during prime time in the high season that the course is going to be crowded, and that means 4 hour rounds will be a rarity. On our 2 9 hole short courses and one 18 hole par 72 course, our facility has recorded 140,000 paid rounds in a single season... and even when we can play in winter, the tee time window is very short between frost off and sundown. Most of that play happens in a 7-8 month period.
So if you play a course which does everything that is politically feasible to maintain pace of play, and the course is still slow, then you pretty much just have to accept it. That means that patience is definitely a virtue on todays golf courses.
Slow Play....
Slow Play.... 
You can beat on this issue with a 9 iron all you want and not do a damn bit of good. You and only you and your playing partners can control this issue. 
Growing old in mandatory but Growing up is optional
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