Try the Olewo carrots added to his food. They claim to have some de-worming properties in addition to firming up the stool. You can never assume anything with de-worming. Those worms can hang on for ages and getting rid of them is simply a matter of luck and exact timing of the de-worming medicine. There is no way to know for sure that he is completely de-wormed, as even a negative fecal can be unreliable if you just happened to hit a negative stool sample. It can be frustrating, but eventually you will get them.
That being said, it is also not unusual for stools to get looser as the day goes on. They normally aren't mudpies as you described, but they will get looser since they aren't in the hound as long as those first stools of the day are (think overnight and baking...)
If the stool is at all like gelatin or has any blood in it, I would say you may still be dealing with worms. If it's just loose and the first stools of the day are otherwise fine, the Olewo carrots added to food will take care of it.