[Rhod the Red]

I don't think Aragorn had forsight. it's just that he knew Moria was dangerious at the time. With the goblins on the rampage. Plus, it seems as if Gandalf's magic is quite limited.

The red ring appears to only be usable with wood around. So there wasn't much chance of using it in Moria.

Aside from that, Gandalf doesn't appear to have any capacities beyond a human. He had his stamina and sword: enough to get through Moria the first time, but a second?