Caesar Cipher

I came across this way of writing codes in one of Dan Brown's book. It was invented by Julius Caesar when he found out that his messages to his generals were intercepted by his enemies.Since no one deciphered the answer to the code in my post titled," Man without Wax",I'll explain it using that code.

The key to decipher the messages is based of the square of the number of the letters in the message.
For example:

WECG EWHY AAIO RENU

The total number of the code is 16. Ergo,the square of 16 is 4.

Rearrange the code words into groups of 4 like shown below.

WECG
EWHY
AAIO
RENU

You could see the phrase,WE ARE WATCHING YOU when u read it vertically. The phrase refers to "NSA".


Again,I'm challenging you to break the code below and those who get the answer right will be treated to Godiva Chocolates.

NPOW NFOS PGMP WFST

hint: 1) Its double coded,one its the Caesar Cipher,the other one is ...........


This contest is open till the 3rd of Oct.

Ps: William is getting a bar of Chocolates for figuring out the method.Will,send me ur contact details pls.