What, more specifically, is the problem?
Personally private property/areas needs to be labeled with a sign (regardless whether or not there is a warp) and then it's free to build as long as you're not too close to someone else's marked territory. That way you know who to contact if you wish to ask permission or is unsure if you're too close to them.
For public areas like cities, yeah let the city builder decide and also place a sign somewhere it's easily seen to indicate who's 'in charge' of the city.
So of the options, I would say #1 is enough, with the added requirement/recommendation of signs to mark ownership to simply make it easier for those passing by to know who to contact should they have any questions. Also, as with everything, how about common sense?