[miellien]

I think that all creatures could sense a power at work in the Wood. It made Frodo and Aragorn feel refreshed, but Boromir uneasy; to say nothing of Gollum. The straight-up "evil" creatures had to be driven in by a greater fear. I believe Galadriel used the ring to create something like the Girdle, although obviously not as powerful. It was aimed at emotions. Evil creatures would feel fear, good would feel hope. Ambiguous characters had to choose for themselves. It doesn't seem that anybody was actually kept out except with conventional weapons.