my friends back home just asked the same. Actually there is no cage or fence, but a guide is mandatory and he got a long forked stick for protection - just in case. He didn't use it.
We've been just lucky that the Water Buffalo died the night before and all that dragons came for feeding.
Usually dragon spotting can be unsuccessful and you don't see a single one at all. But there are always some lazy dragons hanging around the Camp Kitchen on Rinca.