Leave it

This is an especially good command for dogs
who will not hesitate to grab food
or anything they find on the ground

Dogs manage to get their teeth on all sorts of things
that can be dangerous for them, which is why
the leave it command is so important

The number one poison hazard for dogs
is human prescription medication, 
even a single pill can have devastating effects on a dog
There is also the danger of
chewing on and swallowing items
that can get stuck in their throats or intestinal tracts

Unless a dog has been taught to drop
whatever is in his mouth,
he may play keep away or swallow the item
before the owner can retrieve it
A dog that understands leave it
will leave an object alone or let go of the item,
which can then be taken away

Training

Have your dog on a leash and drop
a treat or toy onto the ground
Walk your dog past the toy
just short of where he could get it
As soon as you notice him pulling toward the toy,
sharply say, Leave it and pull him away

When he walks away
without you having to pull him,
reward him with a snack and tell him what a good dog he is
Repeat this with a longer leash and later without a leash,
until he listens to you and ignores the toy
Never forget to reward and praise

First train this with toys 
When the dog has mastered that,
try the same with food and treats