Hi,
Dont worry it wont poison your dog,he is most likely getting at undigested food still present in the poop,which leads me to ask "
what food are you feeding" As eating their own or other dogs poop is usually a sign of them not digesting their food properly.Ofcourse there are other reasons but this seems to be the most common one when a dog is eating another dogs poop

There are a couple of things that may help,these are giving a Bcomplex tablet and digestive enzyme tablet daily,this combination has helped alot of dogs overcome poop eating :) Both are available from the health food shop.
However i would be looking at their food also,if it has a high cereal content and not much meat,then the odds are the food is NOT helping the issue.
Why dont you register(only takes a minute) then maybe you can give a little more info and we can hopefully cure your dogs of this habit before it becomes too ingrained!