My Absolute Most Favorite Cue in the World.

I'm a dog trainer, I love teaching dogs (and their people). I get excited when a dog holds a sit-stay as their owner walks a full circle around them, when a dog gets the 'drop' part of the fetch game and... well... just about every time a dog learns something new, especially when their owner is having fun and sees a purpose. Let's face it, most dog owners want a well behaved dog who listens the first time with every cue, not a dog who does cute party tricks (though those are super fun too).
I'm sure I'll say this about another cue at some point, but right now my favorite cue is by far the "Leave-It" cue. I love it. Seriously. The "leave-it" is great for pretty much EVERYTHING. Don't want your dog to eat your toddler's toys? Leave-it. Does your pup love picking up dried up carcasses of who knows what kind of dead animal during hikes? Leave-it. Is Fluffy always going after the cat? Leave-it. (and maybe a kitty door into the basement or a bedroom).
The leave-it starts out as leaving food alone, I've said it before and I'll say it again: most dogs are motivated by food, so that's what I use for initial training of a cue. It is faded out and your dog will not just work for food, as long as you listen to the food-fade instructions given by your reward-based dog trainer. Like I was saying, it starts with food, which is faded, but during the whole magical teaching and learning process, you can teach your dog to leave just about ANYTHING alone. And they seem to have a ton of fun doing it. And their owners see training with a purpose. And, it's a pretty swell as a party trick. It is everything I love about dog training.
The leave-it teaches bite inhibition to an extent and it teaches self control. Who out there doesn't want a dog with self control?!

*Disclaimer: leave-it is not the same as drop-it. Leave-it is for preventing them from picking up something icky or dangerous and drop-it is for letting go of something icky or dangerous. They are two different behaviors taught in different ways. Got it? Good.

Ok, the good stuff comes next. Here are the instructions for how I teach leave-it. Everyone does it a little differently, but as long as you get the same end result without any force or pain on the dog, it's cool with me.
  

“Leave It” cue

Why: The Leave-it cue is very beneficial for both dog and owner. A dog who can leave something alone on cue is less likely to pick up something potentially toxic to him or her (many household items can be harmful to dogs, remember?). A dog who will leave something alone on cue is also less likely to chew up your shoe or your child's favorite toy!

What: Leave-it is having your dog leave something (treat, toy, squirrel, cat, another dog) alone and ignore it. For example, if my dog is in the kitchen while I am making dinner and I drop a piece of food I ask her to leave-it, since not all people food is good for dogs. On walks, if she sees a squirrel, I ask her to leave-it and allow her to smell the ground for as long as she wants after the squirrel is gone. This is rewarding for her-in exchange for not following squirrel up a tree, she gets to smell wonderful things!

-pocket/pouch full of treats

-hungry dog

-leash, attached to a collar or harness

-quiet, comfortable area

-patience!

How:

1. Start with a treat in your right hand. Place the treat in your palm and close your hand around it. Have your clicker in your left hand.
2. Let the dog smell and see the treat and lick your hand but not take it from you.
3. As soon as your dog stops licking/smelling and looks away from your hand, say “leave-it”, click and treat from your LEFT hand!
4. Repeat!
5. Your dog will get to a point where they look away almost immediately from your right hand and look for the left hand. At this point, switch hands on your dog.
6. Place a treat in your left palm, with your hand closed around. it. Have your clicker and reward treats in your right hand.
7. Let your dog see, smell, dig, lick and chew for the treat, but do not let him/her have it. This side will probably go a little faster, your dog is getting a handle on the game.
8. As soon as your dog stops trying to get the treat out of your LEFT hand, say “leave-it”, click and reward from the RIGHT hand.
9. Repeat!

Tips:

-It is vital that you give the reward from the hand that did not have the treat in the beginning, you want your dog to leave-it, not come back to it later!

-With leave-it, your dog is learning that there are some things they can't have and some things they can, but they have to wait for permission to take them.

More:

-As your dog progresses, place a treat on the floor in front of them and ask them to leave it, then reward with another treat.

-You can eventually place a treat on your dog's paw and work on leave it there!

-On walks, toss treats out in your dog's path, asking them to leave-it as you pass them. After passing by and not pulling to get the treats, walk to the treats and say "find it!" as you point out the treats. This makes walking with you lots of fun since you sometimes point out tasty things!

-Once your dog is really good, try the old treat-on-the-nose trick, by placing a treat on his/her nose and asking them to 'leave-it' until you say “ok!”

As you can see, the method I use to teach this cue helps with bite inhibition (chewing and biting to get what he wants won't work), and self control (I want that treat but I can't have it, at least not right now.)

The sky really is the limit with this one, what's your favorite cue?