I rather like Helm. Strength and Protection(can't remember his other two) are good domains and grant some nice spells and the granted powers are fairly powerful.
Make it easy on both your player and your self and suggest something like a cloak of resistance. And for extra laughs make sure to make liberal use spells like Tasha's Hideous Laughter up until the point that he gets the item =)
In the group I play with we do something similar but what we use the grenade rules in the PH. It's only used in cases like what Rydac stated and when it's in agreement by players and the DM that there's not a clear line of sight.