Was reading one agent, Svoboda I think, talk about how free agency comes in waves. The frenzy of the first day, and then it dies down, and then there's a second wave for the next tier of players, etc.
I imagine that Shero might be active in the trade market during this second wave, as teams that don't fill their needs on the ufa market look for other options. A guy like Niskanen would fit into the 2nd wave... though looking at the UFA defense out there, lots of over the hill types.
The best D are probably Gilbert, Hainsey, Kostka, Zidlickey, White, Lydman, Murray. Shero could probably get good value for Niskanen, who at his age, is as good or better than the crop.