I think you misunderstood me. I am talking about the scenario where during mid or lategame, an AI that you're at peace with comes and founds a new city near your borders, where there are maybe 2-3 usable tiles (but he does it anyway) you don't wanna dow him because let's say, you want to deal with other AIs first or you just want to stay friendly. But you don't want that city nearby as well because it will cause problems later when you DoW him since he can move units and strike your capital which is far from your main army.
That's actually easier, if you see someone coming close then, then cash buy the key tiles out to 3 hexes before he plants so he won't steal any important tile that your own city could have worked.
There is also parking units where you think he might found and the related unit wall tactics.