What I've done with my dog Legend is I've taught him "Trade". So say he's running around with something he shouldnt have I say "Legend Trade" he drops it I say "good boy" and give him something he might want better. Like a new toy(I always keep new toys in the closet), a treat. He knows both drop it and trade. So maybe you could use the same method.
Orson has a hard time with this too.
If he's guarding the toy, i've taught him to "back away" so
i can grab it.
But if he has it in his mouth, about half the time "leave it" will work.
My problem with the trade out, is when playing fetch i dont know
which one he will chase. If i throw the alternative toy, he might still
want the old one or vice-versa... :? aggrevating cause i have to
go fetch myself the one he wouldnt chase!
I find that buy using food, that this is a very easy thing to teach! Just be sure that in the begininng you show the dog the food so that it knows you have it. Dog will probably spit out the toy as soon as it sees the food if it has good food drive and not already full from just eating. As the dog starts letting go of the toy, say the word you use "drop it", "out" or whatever. Eventaully you will no longer have to show the dog the food and eventaully you will only have to reward the out intermittently.