In my experience, rock stays pretty much where you put it. The more you drive over it and compact it, the better it will lock together. I've never heard of rock coming off a gravel drive unless you drag it off.
I'm totally confused at the justification of putting in curbs on a driveway. What will this accomplish?
If it's a look you want, then by all means, spend the money, but otherwise, save your cash for something else.
Eddie