Ya know, what you say about the salt is interesting. I found a mineral salt lick (it looks like a big rock and you put it out for cows and sheep and deer) and put it in my backyard. It's actually from the same mine that my own ground up Redmond's RealSalt is from. I keep forgetting I bought it! I got it so that my dogs can lick from it if they feel a need to.
I am going to stop putting salt in the Iodine bowl. Perhaps the dogs are only "in it for the iodine" as they already have a salt lick in the back yard.
The salt lick is so far back there I can't see whether or not they're licking from it. But they know it's there, and that's all that matters. It is also in a place where birds can't poop on it.