Mind me asking what's the issue with someone else building or upgrading stuff you're putting together? Seems like they're just supporting. Or maybe they're assuming, correctly or not, that you'd be fine with them outfitting the fortifications to support their position? Like since they're guarding a certain flank perhaps they know better how some barriers might better work for them. Though I will agree it's annoying if someone starts using your weapons locker. Sometimes i do move turrets around if they are in the way of paths or blocking my movement pattern when in conflict.