Is erasing free memory securely enough to sell MBP

I am selling my 2011 MacBook Pro with AppleCare on eBay. I have my information backed up via TimeMachine. I was wondering what steps to take to securely delete my information from the MBP. There is an option in disk utility that will erase free disk space by writinig over the data X amount of times. If I delete my account and set up a new one, then delete all the free space with disk utility, would this be enough security for me to be at ease selling my MBP? I am running the latest version of Lion.