Sorry to reup this thread, but here's a similar situation i had to deal with...
Have an 800 acre lease. Have to drive about 8 miles of dirt roads to get to our north boundary gate. The landowner we lease off (the drummond ranch in oklahoma, same drummonds as the pioneer woman on tv) of has buku land, and owns almost all of the land on both sides of that 8 miles of dirt roads.
When the hogs got really heavy in the area, our landowner told us to shoot every hog on sight. Going down 8 miles of dirt roads, you're likely to see a hog. She was telling others to do the same. One day my son and I pulled into our north gate, drove about 100 feet where the dirt road turned to the left behind the treeline. This road is not good, almost 4wd, so we were going pretty slow. Next thing we know, bam bam bam bam, probably 15 shots, and sounded like they were coming from the road, and in our direction. We waited for a minute, turned around to go back to the gate, and the truck was still there.
I pulled right up to this truck, about a foot away from his front bumper, and got right out. Not armed of course, and prob a stupid move, but I was in man mode. I wasn't a complete dick, but this guy knew I was serious. He said it was him, and he unloaded his glock 40 on a sounder of hogs crossing the road, going our direction. He said he had no idea we were just on the other side of the treeline, maybe a 100 yds away. His excuse was that he also leased off the drummonds, and he was also told to shoot every hog on sight, so he did. He was very remorseful, apologetic, and sincere, so my anger faded pretty quickly.
But the main problem is, and some of what you all are talking about in this thread, is that he fired his weapon into someone else's property, not knowing if there was anyone, or stands in his line of fire. He did realize this mistake, and owned it completely. Since then, I've met and talked to other hunters that hunt around us on the ranch, found they were told the same about shooting hogs on sight. Half of them said they only shoot at hogs on their property, and certainly wouldn't shoot in a direction without knowing whats going on in that direction. The other half said they'll stop and shoot them any time, regardless of who's lease it is, cause they were told they could. These guys said they did understand my safety concern, and wouldn't shoot when "driving past our lease" Whatever...
The solution was simple. Called my landowner, told her what's up, and she called everyone and clarified that no-one should shoot towards anothers property like that, hogs or not.
It's all fun and games until someone loses an eye, or worse. That guy who did that to us didn't have ill intentions, was really a decent guy in the end, and thought he was ok until we showed up in front of him like we did. It all made sense to him in the end, thankfully nothing bad happened, and I don't expect he'll ever do that again.
That all being said, I think it'd be best to address it head on with the offender, before something real happens. You don't have to be a dick about it, just real. You'll prob see what I saw, with half completely understanding and the other half, it seemed they felt entitled, and I'm not sure my safety point was taken seriously. Hopefully your guy is reasonable.