Stone's an interesting one. He's one of the few options I'd feel ok with having fill Sekera's shoes. He's a rightie and was a legit #3 dman. If he can bounce back from the injuries, he could be an absolute steal. The thing is, what do you pay him? Something like 5 years @4-4.5 is fair for what he was. 1 or 2 years @2-3 is fair for what he was this year. He'll want the former, we'd try for the latter.
I think 4 years at 4m per gets it done, and I think he's worth about that. He and Sekera would form a great 2nd pairing, IMO. Plus he's been around for a while, so he can help hold the fort on the 2nd pairing being paired with Nurse or (probably, IMO) Reinhart until Sekera is healthy enough to return. You don't really want a 2nd pairing of Nurse or Reinhart and Benning, as that's quite an inexperience pairing, and I think they would get picked apart.
My first choice would be Green from Detroit, and extend him for 3 years at 4m per. But if that can't happen or doesn't happen, then I think Stone is a pretty realistic and acceptable 2nd option. I think both are certainly an upgrade over Russell, who probably still thinks he's worth 4 to 5m a season, or whatever, while bringing no offense. Good luck buddy.