Patience.....

..... is the greatest Tool you will every wield as you work with your dog.  No matter what personality, breed, age or size you may have, if you aren't being patient, nothing will ever work.

Taking a deep breath and thinking about something else while you wait it out in the 'baby stages' of teaching 'leave it' is not only good for you, it is necessary.  In case you're wondering, baby-stage leave it is where you hide a treat in your closed hand, keeping another treat in the other hand, but tucked behind your back...You present the first treat, close your hand and ask for "leave it," then you wait.  While your dog is pawing and licking, and nibbling and biting at your hand, remain still.  Don't move y
our hand, don't giggle, don't say 'leave it...leave it...leave it..."  Say nothing more; you already asked him once to Leave It...Just be patient.
The moment he finally gives up and loses interest in that hand with the treat hidden in it, say "Good" and give the treat from the other hand. Never (!!!) allow the dog to think you allowed him to have the one you told him to Leave.  Always make him believe you are rewarding with a different treat/toy.  Stage One Complete.

I have worked with hounds that have taken upwards of 4 or 5 minutes of focus and digging at my closed fist, while I look off into space, ignoring that my hand has so much slobber on it, I'm gonna need more then a towel.  Yes, this takes a bit of pain tolerance, but the payoff, is that you have just patiently, peacefully found your dogs' attention and the next time you try it, it won't take nearly as long.

Working through the four stages of teaching Leave It (well, I use four anyway.....) will ultimately net you a dog who can 'leave' a guest alone, not pick up that nasty piece of McDonald's wrapping on the sidewalk, chase your neighbors' cat, or chase a ball into traffic.  I can leave a plate full of chicken wings on my coffee table, and know they are safe from the roving mouths with wagging tails...So long as I ask them to Leave It.

Using these baby-stages to get to the other, more difficult Leave It's can also avoid unnecessary force being applied.  There are some "trainers" out there who are still using the ol' corrective collar and a good hard yank to try and get this behavior.  They feel it is 'quicker' or they just haven't learned how fast it goes when you use these baby-stages first.  The amount of force required for this to work on a grown, strong or large dog is certainly more then most people are willing or able to apply.....I certainly wouldn't want to use that.

Patience, and some baby-stages.  Before you know it, you can set that plate down to go get a drink, and know it will still be there when you return; with food still on it.