wild FENCE appeared!
Now on the serious side of things I hardly understood anything of what you tried to explain but I'll assume you see that fence even though you're certain no one else sees it, right?
If so, the first thing that comes to my mind is if your GTA:SA where your MTA client is hosted has any mods with buildings and stuff like that (Aliencity < as an example)
The other thing is just that someone built something there, do you see it always, or you've just seen it once and instantly published here?
Right now there's nothing there for me, so if you see a structure there, its on your end somehow, if that fence is still there once you get back ingame you will have to re-install your GTA SA as it'll be the easiest way of fixing that.
If I was you i would immediately contact the CIA..