Indoors we use red tape generally. Outdoors I have seen, stakes, sprayed lines, and rope like you mentioned.
Interestingly, if you do the geometry, if you're trying to see less crowding cover, you would have to be more generous with the line.
Look at this incredibly detailed diagram:
T1
wall
S1
S2
S1, if leans out will be able to target more area in front, vs. S2, if both can only lean out the same distance. (use a ruler and 3mm for each to see). I've found this in practice as well (as I don't like to crowd barriers).