This is a good idea for a thread, Brian, so I promise I won't make any flippant remarks about "The 30/06 Solution."
Leading by example is certainly the best way to instill proper trail etiquette. It's easy when, for example, a bunch of Expo people take out someone new to the activity and point out the correct way to drive and treat the land. It also helps when websites such as this one make a point of truly promoting land use ethics, rather than just sticking a token Tread Lightly banner on the home page and then allowing irresponsible posting and photos.
But it's much harder when you happen across a group of what you're initially inclined to call yahoos driving where they shouldn't. The Tread Lightly training stresses a friendly, we're-all-in-this-together approach to point out the error of their ways, and that might work now and then.
But all too often the people you have come across really are yahoos. They know perfectly well they shouldn't be doing what they're doing; they simply don't give a damn, and will tell you to mind your own business in less than polite langauge, no matter how obsequious you've been. I feel this is the real challenge faced by responsible backcountry travelers. And frankly I don't have an answer to it. Calling in law enforcement would be the best approach, but we all know that's impractical at best, and usually impossible.
As an individual you are helpess in such a situation. In a group you might get better results with polite but firm confrontation, but it's still a crapshoot. Sorry, didn't mean to mention shooting.
We get a lot of backcountry users near our property. It's a generalization, but I maintain that truck and sport utility drivers are most likely to obey the rules, ATV riders significantly less so, and motocross riders least of all.
Case in point: Our property crosses a wash below the house. When we first moved out we left it as is, and put a sign asking people to stay in the wash because there was a house nearby. After coming home to the fourth or fifth set of ATV tracks coming up into our yard, we realized that wasn't going to work, and we reluctantly fenced the wash and put up a No Trespassing sign. A perfect example of consequence for everyone following behavior of a few.
Where the fence crosses the wash is very narrow, so I put up another Private Property sign about 50 yards down the wash at a good turnaround spot. Again, this is just our experience, but about 9 out of 10 large 4x4 tracks turn around at the sign. Probably 3 out of 10 ATV tracks do so. The rest just go right past until they hit the fence. And three times now riders have forced their way under the fence and ridden right across our property.
I enjoyed catching one guy in the act of doing so. I just happened to have an AR15 slung over my shoulder at the time. He was abjectly apologetic, but obviously only because he'd been caught by someone carrying an assault rifle . . .
Roseann confronted two coming up the trail to our house. Both of them turned around when they saw her and raced off. Needless to say that doesn't leave one feeling comfortable.
I believe all ATVs and bikes should be required to have a license plate, so identification can be made in such circumstances. It doesn't do much good to describe a full-face helmet and leathers.