Teaching Your Dog to Drop Food, Toys and other objects from their mouth

This video takes a look at an alternative way of teaching a "drop" compared to the usual swapping based techniques. I have found it works really well.
I would suggest that you do not use this with dogs who are "protective" over their food or other resources but work with a qualified behaviourist / trainer who may use a similar exercise if they see it to be beneficial and/or appropriate in your particular case.