This video explains how to teach 'leave it' using the clicker training method. Not only is this method the most effective, but it also builds a dogs desire to find and interact with their owner OVER distractions. Using punishment while training leave it, diminishes yourself as something reinforcing to interact with.
P.S. Please feel free to link to my videos BUT please do not use my videos without asking to promote YOUR dog training videos and products! (I cant believe this has happened! But it won't stop me making free videos for everyone else!)