I have some suggestions for you. If your dog actually eats any amount of litter, it will clog him up pretty bad. As disgusting as it may sound some dogs like the taste of litter and puppies in general eat everything you do not want them to eat. Eating litter is a difficult behavior to correct.
Do not use the litter crystals or clumping litter or any type of cat litter unless it is 100% natural.Get some rabbit bedding at your pet store or online, the compressed sawdust type. It is pellet shaped and dissolves on contact with anything wet, which means if your dog eats it, it is not harmful.
The next suggestion is not to use litter at all. Use disposable training pads instead.
You may want to take a look at a couple of litter boxes that do not use litter at all - if you go to my web page at dog litter box you will find links to "PETaPOTTY" and "UgoDog" - these are both good alternatives. You will also see a link to training pads if you decide to go that route.