Neon, you train leave it by setting up something a pup will be interested in, normally a treat, and then rewarding them for not taking it. My comment was purely in response to the way in which Max2011 has been told to train, whereby the puppy then gets the treat it has left - as he has found this leads to a pup who thinks they will eventually get whatever they are being asked to leave. By training it by giving a different treat, and putting the original one away, the pup doesn't make that association.
You can then generalise the behaviour to ask them to leave other objects in return for a treat... and eventually fade out the treat.