I have noticed that percula clownfish tend to spend a lot of time swimming rather high in the tank at first. This is my personal observation, but slowly, very slowly my clown worked his way down. As long as you don't have anything that is aggressive to it he'll find himself a nice spot among your live rock to relax. One thing to possibly consider is getting him a mate, I got a second smaller clown several months later and the two seem so much happier now. Just be careful about the size you pick, if they are both small you should be ok, or atleast try to make sure the new one is smaller.
I have heard of clownfish taking on a variety of things as a host, corals being a fairly popular choice but the most interesting was a feather duster hosting a clown.