Sometimes, despite all of your hard work, your puppy might slip up and eliminate in the house. If you catch him in the act, make an abrupt noise to stop him then quickly bring him outside and give him a reward for finishing in the right spot (it’s okay if you take him out and he doesn’t go). Don’t punish your dog for the accident; simply clean it up with an appropriate odor eliminator and vow to watch him more diligently in the future.
Seeking professional help doesn't mean ditching your DIY training program. You can find a professional dog trainer who offers private training sessions, and some trainers even offer online sessions. Many dog owners prefer to join a local dog obedience class so they will be under the supervision of a dog training instructor without the higher cost of private sessions. Plus, classes challenge your dog to learn around the distractions of other dogs.
The process is the exactly same for older dogs as it is for puppies; prevent accidents from happening by using baby gates and a crate if possible, create a predictable schedule, learn to recognize your dog’s potty signals, accompany your dog outside and immediately reward for all outdoor elimination, properly clean any accidents and supervise your dog until you’re sure that he understands the rules.