Hello, Your cat is definitely trying to tell you something. He is probably going outside of the box due to discomfort or urgency. It is possible the soft stool will resolve with a different diet (if this is the first time he has experienced prolonged soft stool). However, there are many causes for diarrhea in cats including: dietary ingredients, stress, intestinal parasites, other infections (bacterial or viral), hyperthyroidism, immune driven issues and possibly cancer. It is most important that your cat is eating well, however, we also want your cat comfortable. Your cat needs a thorough exam and most likely blood, urine and fecal evaluation. I hope this information is helpful. You may call me at 813 877 6369…Good Luck, Christine Simon D.V.M.