The Lucians wanted to hide this clue in a place where there was heavy security so that it wasn't easy for the other branches to steal the clue. However, if the Lucians would have just build a huge building to keep the clue in, it would have been obvious that there was a clue located in that place so the Lucians went to the place where they have the most influence...the government. They convinced government officials to allow them to hide the clue in Fort Knox for safe keeping.
Clover is a weed-like plant that originated from Ireland. Clovers typically have three petals but once in a great while they will have four or possibly even many more. Because clovers with more than three petals are so rare, they are said to be symbols of good luck.