There is a good deal of info out there as to why this is correct.
The 'poor mans copyright' is easily faked.
Moreover, it is technically copyrighted as soon as the work is put on a tangible medium, named, and given the copyright symbology.
The number 1 thing to do is file it with your country's Copyright Office.
Linky to US COPYRIGHT OFFICE
They keep the record and is the textbook way of finishing off your protection.
Choosing not to do this, the second best option is to have AS MUCH PROOF THAT YOU CREATED IT AS POSSIBLE.
Put a song on a CD and label it.
Do the poor mans copyright
Put it on the internet
Stow it away with witnesses that can notarize.
Give out copies
Every bit of proof will help you in the court of law.
But best to just have it recorded at the US Copyright Offices if you are that intent on protecting it.
Newgrounds operates under a CC license.
I'm sure you'll hear more about that below