Hello, my name is***** and I have over 20 years of experience as a veterinarian. I understand your concern about Samson's behavior. It's no fun to find stool where it shouldn't be.Cats stops using their litter box to defecate for a few reasons:1) They don't feel well and associate pain with their litter box so go elsewhere hoping not to experience discomfort.2) Their litter box is dirty, hard to get to or in or out of, it isn't big enough to move around and get situated to comfortably pass stool, they don't like the litter in the box, or they don't have enough privacy in it or feel trapped in the location it is in. If the box is upstairs or downstairs from where they normally sleep, or in dim light they may have difficulty getting to their box.3) Other cats (can be indoors or outdoor strays), dogs or people are scaring them when they are in the box or trying to get to the box.4) Social stress and overcrowding. Cats in the wild do not live together. It is socially stressful for them to have to be confined together. That is likely why many cats stop "marking territory" once they are allowed to go outside. They are less "socially stressed" because they have more room and get more exercise. First I recommend limiting access to the area that he is inappropriately using as a place to eliminate. The longer this goes on the more it becomes a habit. If this has been going on for a while it is likely that we need to find and treat an underlying problem that started all this as well as retrain him.Ideally he should have a physical examination to make sure all is well. Make sure his anal glands are checked, and that he doesn't have parasites (check a stool sample) or spinal arthritis that makes it painful for him to go or maintain his position. If he ever has blood or mucous in his stool, it is soft, hard or very large or small and difficult to pass he may have inflammatory bowel disease, constipation or megacolon which are all uncomfortable. We need to address any medical problems to have hope of retraining him successfully. You also need to make sure that the area that he has picked to go has been cleaned with an enzymatic cleaner, like Nature's Miracle. Although it may smell fine to you, their noses are much better than ours and as long as the odor is there he will be attracted to the spot. Make sure his box(es) is/are spotlessly clean, scoop stools daily, change litter completely weekly and clean the box itself. If the litter box is older than a year get a new one. Many cats don't like odor and an old litter box stinks to them. It might be fine to pass urine there as that is quick but stool takes longer so they are more particular. If his box is covered you might try an uncovered one. Ideally if he is an only cat you should have 2 boxes. I hope they are in different locations and where he cannot be bothered and they are easy to get to. Some cats like to urinate and defecate in different areas and are very sensitive to being interrupted. I know you may have done some of these things already but I list them all to be complete.Make sure he has privacy when he goes, yet also make sure the box is easy to get to and get in and out of. Many cats appreciate low sided boxes, especially as they age or if he is a very large cat. Some cats also like a bigger box to pass stools in so they have plenty of room. The plastic very low sided storage containers that fit under the bed work very well.If you are using scented litter I recommend plain clay litter or plain scoop litter. Most cats find scented litter objectionable. Even if he is an only cat animals outdoors, including strays and wildlife, may be contributing to his behavior. To help ease social stress you can try using Feliway sprays or diffusors. These are synthetic pheromones which mimic those produced to mark areas as safe and many cats find them soothing. You can also use pheromone calming collars as well. See this link for some examples:http://www.amazon.com/Sentry-Behavior-Pheromone-Collar-Inches/dp/B0026JAKWG If these measures aren't enough you can try adding homeopathic calming oral medication called Bach's Rescue Remedy. See this link for further information: http://www.bachflower.com/Pets.htm And you could discuss oral medications with your veterinarian as well such as fluoxetine or amitriptyline as calming agents to decrease his stress. Finally if he does better when allowed to go out you may wish to construct an outdoor cat pen so he can safely spend time outside. Here are some examples: https://www.google.com/search?q=outdoor+cat+enclosure&espv=2&biw=1565&bih=780&source=lnms&tbm=isch&sa=X&ved=0CAcQ_AUoAmoVChMI3YqM_KSBxwIVCFCSCh2hNgOk&dpr=0.9 If you do all this and he is healthy and he is still not cooperating I would confine him to a large dog cage or small bathroom with his food
, water and litter box to retrain him. You can let him out only when you can supervise his behavior. If you catch him going to his "spot" use an air horn to scare him. He must have the negative consequences every time or this won't work. Do this for several weeks until he consistently uses his box. Then slowly give him more access to your home, a little more area each week if he continues to behave.Best of luck with this fellow, and please let me know if you have any further questions.