Even when I run on roads, I do the following:
1. I tell my wife the general route and timeline ahead of time (e.g. "I'll be running around Beef Park for 60-90 minutes")
2. I carry my phone with me in my FlipBelt
3. I make sure the GPS is enabled on my phone so my wife can ping it in an emergency
4. I try to avoid locations with no people (e.g. the warehouse area near my house on a weekend evening). Don't want to run into a drug deal in progress, or pass out and no one passes by until the next day.
5. I wear very light clothing. If I'm going in the evening, I wear a reflective green construction-worker vest
6. I don't 'improvise' trail running, I stick to the script
7. I'm conservative with weather? 102F and blistering sun? Yeah, I'm running 1-mile laps around my house and drinking some water very single mile.
Another person mentioned they carry a whistle they can use as well, which seems like a great idea.
Yeah, I'm probably overly paranoid, but I don't want my wife to worry, and my kids to grow up without me.