Does the shield of force created by the ring of force
shield (Dungeon Master’s Guide, 232) require a free hand to
use, or can I use it when wielding two weapons or a twohanded
weapon?
The item is silent on the issue, so the Sage believes it
appropriate to assume that the ring’s shield functions just like a
normal heavy shield (except for the lack of armor check
penalty or arcane spell failure chance). Thus, it requires a free
hand to gain the shield’s benefit.
Of course, a character wielding a weapon in that hand
could activate the ring after making his attacks for the round
(thus gaining its benefit while enemies attack) and deactivate it
at the start of his next turn (allowing attacks with that hand).
While you wouldn’t be able to use the shield hand to make
attacks of opportunity while the shield was active, you’d
otherwise be nearly as effectively protected as if the shield
were active continuously.