Why should he not be untouchable? No trade made involving him will net us a player near his value to us. Teams with top-pairing defenders on value contracts rarely trade them. Orlov is a core player IMO and I believe BMac would move Kuzy/Vrana before thinking of moving Orlov.
Also, in numerous interviews, he has mentioned how happy he is in DC, with the continuity and playing top-four minutes. He was renting an expensive apartment for years and he was so happy to be able to finally buy a house and settle his roots down here with his wife and newborn. He has also mentioned numerous times how much he loves the org., core, and wants to play his entire career here.
Edit: I want more guys like Orlov on my team. Paid his dues, works his ass off, loves the org. and team, and has developed nicely.