I'm not sure what you mean by below 580 metres but there are a couple of tricks to bounded box..........you have to put your fish/whatever at the level you want it before you put the bounding box script on because it will always drift back. In other words you can't change it's 'y' position after you put bounded box on. Also make sure you have 'no bsp collide' ticked so it can move. If you need some help in world just give me a shout, sometimes it's easier to see what's going on rather than try to explain it.