If you put a cookie in the middle of your livingroom floor; do you have enough verbal control over your dog to not have that cookie eaten? Not too many people can do this; but you should be able to. Having older dogs now it's not something that I use alot but when I need it; it's there.
Leave it, is one of the most important things I teach my clients to teach their dogs. It is an exercise that starts out fairly easy and very structured; which builds to "real life" status once learned. Of course there are things that are more difficult to leave than others. Heck when I go shopping; there are some things I can't leave at the store, some I can.
Leave it, can be taught to very young puppies or seniors who have never been taught the concept although it may take a while. Taking has alot more meaning behind it other than the fact that they are taking everything. If your dog takes whatever they want even when asked not to; then you have no leadership status.
I like to keep my guys on their toes; we all tend to let the seniors slide so every once in a while they get a refresher. We may be watching a movie and I will toss a cookie on the familyroom floor. As all attention is drawn to the cookie I state a very calm "leave it." Attention is then on me, I am controlling the cookie.
Jessie's answer to this difficult task is to look away. It is much easier for her to deal with not eating food on the floor if she is not looking at it. The poodles look at it, then me and realize they aren't going to get the cookie and relax. Depending on what type of food has been tossed onto the floor is the length of time spent looking at the item.
There are times even with my guys that they simply can't bare it; usually because of a new toy in the house. If someone decides to go for it and not listen, a simple enforcing movement towards the item reminds them of who's item it is. There is no harsh words; serious maybe but no yelling, body language works much better.
Give it a try and let me know how it goes; I'd love to hear about it.