How can I keep my pup from eating rocks and mud?

My pup is constantly eating rocks and dirt/mud. I am sure this is not good for her. She eats so much her poo even looks like mud. Is this some sort of deficiency or nervous habit? Is there something I can do to deter her from doing so? I have tried toys while we are outside but she completely ignores them and goes straight for the rocks and mud...Any suggestions?

How old are your dogs?

How long are they outside?

What do you do with them whilst they are outside?

What sort of mental and physical exercise do they have.

What toys (not interactive) do they have to play with instead of rocks eg stuffed kongs, bones etc?

The one thats the culprit is 4 months old, she is outside for maybe two hours alone, we go on about 6-7 walks per day for a half hour or longer. I also have been teaching her commands such as sit, down ,leave it, focus, come, heel, paw,etc. She gets her tuggy, stuffed kong (with treats in it) and a ball outside and like I said she just ignores it. If any of those toys were inside I cant keep her away from them.

A four month old puppy should not be doing a total of 3- 4 hours a day of exercise, this is FAR too much for ANY breed let alone large and/or giant ones..

Leaving a dog outside alone with no one to interact with will result in boredom (if not theft).

So you could try building a digging pit for her to amuse herself with every day by searching for treats, toys etc.

You could not feed her in a bowl but scatter feed her so this occupies her for some considerable time (not on gravel though), or put her food in a tug a jug etc so she has to work for it rather than getting it for free several times a day.

Balls are for playing with PEOPLE with as are tuggies.

How much exercise should a large breed get? And on that note how much sleep should she be getting? She acts like it doesent bother her as she wants more it seems. She comes in from our walks and grabs her tuggy and gives it to me for play. Was thinking about building her a pit (as I saw on "Its me or the dog" ...does that work? I know balls and tuggies are for playing with PEOPLE and I try to play with her outside but she wants no part of it. Also, I live deep in the country so I dont have to worry about theft...and when I said alone I guess I am always looking out the window to check on her to see if she started eating her bone or trying to get treats from her kong. Never heard of the tug-a-jug looking it up now...