If taught with consistency and dedication, dogs can learn good potty manners in short order. Even with good training, many puppies and dogs experience setbacks with accidents inside the house. Some regression is normal, while other causes for regression can point to medical issues. If you'll establish a consistent daily routine for your dog, know his normal eating and potty habits, and set realistic expectations for him, he'll be much less likely to suffer setbacks.
Once your puppy has learned to potty outside, expect setbacks in his training with the onset of adolescence. Varying from breed to breed and dog to dog, the dog's "teenage years" generally occur somewhere between 4 months and 3 years of age. During this period, his hormones rage and he can become easily distracted, making him forget his potty manners. Young dogs experience learning plateaus, suddenly seeming to unlearn the things they've been taught. At this stage, your dog likely hasn't fully mastered trained behaviors. If this occurs with your dog, apply strict house rules and reinstate potty training from square one. With your consistency, your dog will normally correct the behavior within a couple of weeks.
If you have an adult dog who suddenly begins having accidents in the house, thoroughly examine all aspects of his health and environment to determine the cause. Sudden changes in his daily routine -- feeding schedules, the amount of time he spends alone or the addition of new family members, human or animal -- can all disrupt his potty routine and lead to accidents. If your dog's schedule has remained consistent, visit your veterinarian to rule out medical causes such as bladder infections, kidney infections or a disease such as Cushing's. Meanwhile, older dogs may begin to lose bowel and bladder control with progressive age.
Keeping Puppy on Track
Expect most puppies to demonstrate reliable potty habits by the time they reach 4 to 6 months of age. A few dogs may not achieve full training until they reach 8 to 12 months of age. Set reasonable expectations on the amount of time your dog can hold his bladder and set a regular schedule for potty breaks throughout the day. Realize that a dog forced to remain in confinement beyond his ability to hold his waste will learn to soil his sleeping area. As a general rule, don't expect your puppy to hold his bowels or bladder any more hours than his age in months. For example, a 3-month-old puppy should be able to wait three hours before going outside to potty. Reward good behavior with lots of praise and treats and discipline sparingly.
Adjusting the Adult
As long as medical reasons have been ruled out, re-establish a reliable routine with your adult dog. Revert back to basic potty training, keeping him confined or under close supervision while inside the house. Take him outside for regular potty breaks and reward successful elimination outside with treats. Maintain a consistent feeding schedule, taking him outside 20 to 30 minutes after his meals. Don't free feed your dog, which can lead to inconsistent potty habits. Finally, thoroughly clean up any accidents using an enzymatic cleaner to remove all traces of his scent from carpets and furniture. Avoid cleaners with ammonia. Since pet urine contains ammonia, such products can actually encourage him to soil the same area again.