When you play as ghost and have the bomb stay up the top bit on the map and head to B site, when you get there you should be looking down on the huge circle light thing. Fall down on top of it making sure no enemies see you, if you dropped down from the walkway that is broken turn left and slowly walk to the edge of the circle structure. Look down and you'll see that there is a little ledge on it, keep slowly going forwards and when you drop down keep holding forward down. If you did this carefully and are on it plant it immediately and run away. GR will never find it and even when they do they can only get up there the way you came. They NEVER work out how to get to it, this has worked and won the round every time I have done this. I will post some screen shots soon to help.