I use food as a tool in teaching. "Teaching" being the aquisition of behaviour. Once a behaviour is learned, food rewards (or reward in general) transfers over onto life rewards - the dog doing A to be able to do B. A couple of exceptions to these are:
- Recall. By this I mean my "drop what you are doing and come now" recall, not my "okay, we're going now" cues. For dogs that love food I will always use high-value food rewards to teach and maintain a strong recall. For something so important in a dog's life, I am willing to give up a piece of liver if my dog comes each and every time.
- Fun tricks that aren't typically useful in everyday life. Things like cleaning up toys, or spinning. I will occasionally pop out a minor food reward treat for that.
But in speaking only for myself, I work with what the dog wants, and try not to let my own thoughts get in the way too much. So I use a wide variety of toys, touch, play, and treats, to get to my goals. Some dogs I've taught basically only with toys. Some dogs I"ve taught with a combination of all of the above, depending on the situation. Some dogs I've used mainly treats for. I let the dog tell me what is most reinforcing, and I use it. SUPER high value items, regardless of what it is, comes with SUPER performance. Medium value rewards come with medium performance, and lower value rewards come for ho-hum performance.
For Gaci, for instance, she loves tug, she loves to chase things, she loves to play "catch me", she loves to run free, she loves food. When working she's not that into touch, and while she enjoys touch it isn't high on her "reinforcement" list - mainly because I use touch a lot in the form of affection, and I don't tend to use it as something a dog has to work for. Affection is something I give freely, independent of behaviour (I consider affection and attention separate things). I usually use affection along with all forms of rewards, when rewarding, so I don't consider using it on its own.
For Shimmer, now, she loves affection and attention. She thrives with it, and finds it normally very reinforcing. This girl will work with you for lovin' alone! She also loves food, and likes toys in a so-so manner. But most of all she likes knowing her person loves her.
So I use these things with each dog differently, I don't take a "one reward fits all" approach with animals, as the most efficient teaching and learning comes from using what the dog actually cares about.
In terms of food, though, I have never experienced what you describe above. Now, perhaps it is because I use a variety of reinforcements, but even in dogs I've worked with with mostly food, I have never had dogs "depend" on food. Dependence on food is, IMO, a failure of the use of food as a reward, rather than the fact that food was used. It's no different than having a dog dependent on a certain toy, or dependent on touch, or dependent on anything. Dependence is never a good thing no matter what you use as a reward, so if you have dependence, chances are your goals have gone awry somewhere. My dogs will do the behaviours they know despite the reward they may get, not knowing which reward they may get at any given time.
Dependence on food (or anything) also I think inhibits learning, rather than promoting learning, as it diverts the dog's focus and attention away from the task at hand and onto the depended item.
Your dog is not what I would consider a "normal" dog, in the sense that she has an abnormal fascination with food (going by what you have described to us). So you really can't based an entire book of knowledge on this one dog. It's extremely valuable information, as you now have the experience of working with an animal that has something that goes beyond "reinforcer", bordering on "addiction". This will give you valuable information and insight into future work with dogs. But one exception, as you know, doesn't make it the rule. I have not worked with personally, although I have known, an actual food-obsessed dog. So one would say you have a foundation of knowledge and experience that I do not. Now, I don't know if I'm just lucky, or if there is a reason my dogs have not become food obsessed. I lean towards the latter, since I have experienced in my personal life a very large number of dogs compared to the norm, so my sample size is quite large.
My basic experience in animal teachings, of various breeds and personalities, has not created animals that are dependent upon a certain stimulus. So I don't for a second believe that as a rule you create a habitual environment in which a dog depends on the food. I wouldn't say your dog just finds food "a high value", it goes a lot beyond that, beyond value as a teaching tool, and into something that for this dog, creates an imbalance and altered mind state. It's like heroin for a drug addict - it's not just a high-value reward, it's goes much deeper than that.
Food is not a requirement for a well-mannered dog. But it's something that I use as a part of my toolkit when I feel it would be the best option. You hvae found that praise works best for Penny, that to me sounds like you have done your homework and found a proper reinforcer for her. Keep at it, and keep using it. That's awesome! But I think if you have more dogs in the future, the more dogs you experience the more you learn that every dog has its own likes and dislikes, and will communicate that to you as you share your life with them.
I agree that food can be the easy answer for some, if they do not look into all of the possible things their dog (animal) finds reinforcing. And engaging in good discussion with dog folks will hopefully reveal that fact. But if the dog learns well with treat, is not dependent on treats, is not unhealthy due to the treats, then by golly it's not my job to say they should try to use toys or praise. On the other hand it's not just the easy answer for everyone. It is used part and parcel as a package in which to teach our animals. I think as soon as some folks hear "food" they picture these treat-eating machines that function for nothing else, and live for nothing else, when in reality when I say "use food rewards" it might be for every third behaviour, or every tenth, or for two teaching sessions and then not again. It's really quite variable, and situation and dog-specific.
In terms of competition, there is competition amongst all species for all things. That's how life is. Food is one of those things. But there are no huage problems here, we can throw lettuce on the floor after supper and all 14 dogs will happily eat without so much as a grumble. I'll place 10 Kongs or so down (not all dogs care for stuffed Kongs) and not even have to blink at whether there may be an issue, it's a non-issue. Part of the competition in dogs is inherent, part of it though is simply whether or not the dogs feel they need to compete for food. In our home there isn't a lot of need for competition, the dogs feel secure that they will get food so they don't have to fight for it. I'm proud to say that in the home so far I've never had to interfere when it came to food between the dogs.
You might try feeding in crates and see what happens. Most of the dogs here eat their meals in kennels (four eat in the open kitchen), as it's just easier, and it has also had the benefit of classically conditioned them to really love their kennels. It's always worth giving it a shot if you think it might make a difference!