anirtak,
I live on the Island of Jersey, where Gerald Durrell founded the Jersey Wildlife Preservation Trust JWPT (I know you didn't know, just mentioning it). I try and go up their every couple of years, usually to show relatives and the like around. The trust, has the right idea, give the animals as good a life as they can. They have even allowed a group of Marmazetts to life in the tree tops.
Your suggestion about the rocks, is a good one. One I hadn't thought of. Thanks.
Love and light
Japestar