Fawkes has had a long term problem with extremely soft stools bordering on diarrhea.  He's done different diets but what IMHO really helped has been pro/pre biotics.  Our 2 tenants are 4th year vet students and they have passed on some sample packs of various digestive support/digestive aids or whatever each company calls them.  The first stuff we tried (I forgot to write down the name/company) wasn't that good but Synacore (van Beek) and Digestive Enzymes (Naturvet) have really made a difference.  He still can get soft stools but it's maybe twice a month instead of everyday. 

The funny thing about Fawkes' improved digestive output is that picking up our backyard has gotten more of a challenge.  Fawkes never seems to poop in the same spot; can vary between 1-3 poops a day and often poops in stages (poop, takes a few steps, poop a little more, take a couple steps, finish.) Our fenced in backyard is about 1/3 an acre and has 11 trees.  With all that shade,  growing grass was futile and so to keep it from becoming a mud pit, the ground is covered with wood bark/ wood chips of various sizes.  We have 3 kinds of spruce back there and they each drop cones of various sizes.  The trouble is that there's a lot of stuff on the ground that is roughly the size and/or shape and/or color of firmed up dog poop.    The soft stools were gross but they were light tan and so big that they were easy to spot.  Finding Fawkes' poop in the mulch is like looking at one of those "hidden eye" images, if I look at the right area with my eyes slightly out of focus - whoa! - there's a poop.