Abby did this...we tried Forbid to no avail, and we tried Deter, which I THINK worked. It didn't work until we did the double doses though. They tell you if the normal dosing hasn't worked after 2 weeks, to double it. I cannot be positive that she is completely cured bc there's no way of knowing what she does in her crate while we are at work!!! But there's never any remnants to show that she may have gone and she goes as soon as we get home, so I think we are good.
While we were researching, I also red about meat tenderizer being used (vet also said this) and pineapple juice (which he never heard) and the all purposeful pumpkin. The vet said that different things work for different dogs...it just depends on what "taste" disgusts them.
Causes for it, as I read...inadequate nutrician from food (so look at the type of food you are feeding), inadequate amounts of food...leaving them hungry, not properly digesting the food...meaning they need more nutrician, which is apparently where the meat tenderizer comes in...it helps break down food more meaning they get more nutrician out of it (and makes their poo taste bad).
In our case, I am convinced that it had to do with her housebreaking issues. She was very hard to housebreak and I think she started eating it so she wouldn't get yelled at for having gone...hiding the evidence!!! "Yelling" at her (not really yelling, but more than a simple "NO!" and leading outside was a method we tried for 2 days after 5 months of trying to housebreak her according to the books! It backfired clearly!