I had a similar issue: I was tripping over a fire ring that was present at one campsite we used last year.
I left one of our flashlights on, shining inside the fire ring until we packed up the next day. I fiddled with the flashlight setting and orientation until I had it mildly illuminating the ring enough to be obviously visible but not enough to be obnoxious.
You could do something similar, leaving the flashlight at one end of the line or the other, or perhaps hanging from the middle of the line pointing down. Even if the line itself is not visible, as with the hanging light pointing down, make sure everyone knows what the purpose of the light is so they avoid it. Also remember that if you put the light at the far end of the line and face it toward the tent that may cause problems for the tent occupants.
- Obviously plainly visible at night
- Provides extra light to the area
- May be too visible inside the tent
- May attract unwanted attention
- Leaves a flashlight unusable for other tasks unless you bring an extra
- If you bring an extra, requires more tools
- Can run out of energy (though good flashlights and batteries should handle short trips fine)
I get cheap and mid-priced flashlights. Even the cheap ones can generally last all night. The mid-price ones with multiple power settings generally last all night even on the brightest setting, and on dimmer settings could last for days.
One of our hammocks has a line around its rim which is laced with dim lights and it has a battery pack at one end. Its purpose is for helping see the location and orientation of the hammock at night. If you can get a similar line, maybe you can use it as a guy line. Ours might not be able to bear any significant load, but you might be able to find some that can.