I couldn't agree with Lori more. A detailed itinerary with a trail map ("trail 101 to trail 203; take 203 to 187, then 187 back to 101...") is part of the key to safe soloing. The other part is leaving it with someone who is absolutely reliable, and will call authorities a minute or two after your "drop-dead" return time passes. And, be sure to include the emergency numbers (local sheriff, park or agency management, SAR, etc.) on the written itinerary. Sometimes, in addition to the person at home, I've sent a copy of the itinerary to the management agency and also left a copy on the seat of my car.

Along with the itinerary, establish a time by which you will call the person you leave it with to tell them you're off the trail and heading home. When you establish that time, be sure to allow for a late start the last day, some extra time to hike out (there's always the chance you'll find some view to linger over), and the drive time to get back into cell phone coverage.

For example, I know I'll be up by 6 and on the trail by 7, which will put me at the trailhead by 9. Let's call that 11, in case I oversleep or have a second cup of tea. Another hour back into cell phone range means noon - and let's add another 3 hours, just because. "OK, Karol, if you haven't heard from me by 3pm, call the emergency numbers on the itinerary and have them start looking for me."

I used to hike solo a lot. For those trips, I never did any off-trail; if I became injured, I wanted to be very easy to find ("Hey, here's a guy lying here in the middle of the trail - is he the one we're looking for?") I also specified my most likely campsites in the itinerary.

I now rarely travel alone. I'm not afraid to do so, I just find that nowadays, I enjoy company. But, maybe once a year, a night or two all on my own is a nice way to recharge the batteries.

For more insight on hiking alone, read the first couple of chapters of Colin Fletcher's Complete Walker IV - there's a lot of good info in there on leaving a plan. (He did often leave an itineray that consisted of "thataway" or "mucking about" as his projected route of travel, but always made sure he contacted someone by the time he said he would. At least, that's his story.)