I personally put "spot taken" on my ISS when I leave the place for a few hours, but nobody respects that, but this is fine, I start looking for a new one.
No DD, dead DD = free spot.
The real problem, I think, is that some people come to an active spot, it doesn't matter if there are people who is farming, pretending to perpetuate themselves there. In Naia a clan does that, stealing mobs.