You should always accompany your puppy outside for potty breaks. You’re there not only to ensure that he actually goes, you’re also there to reward your puppy with a treat for going in the proper spot. Wait until your puppy finishes eliminating and immediately give him a tasty reward for a job well done. If you wait until you get back in the house, your puppy won’t make the connection between his elimination and the reward. 

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.
Young puppies can’t hold their bowels & bladders for long. If you come home to find that they’ve had an accident in there it’s quite possible that they can’t hold it that long. Generally puppies can hold their bladder for about one hour per month of age. So your 3 month old pup can probably only hold their bladder for about 3 hours. If you’re going to be away at work for long periods of time see if you can get a neighbor, relative or dog sitter to come over to let your pup out during the day.
A training class is not there to train your dog. Its purpose is to teach you to train your dog so you will need to be committed to train your dog for short sessions (5 minutes) several times a day rather than just simply turn up for classes! This little bit of training everyday will be repaid with a lifetime of living with a well behaved dog. You will also learn to avoid problems before they begin as well as receive help to overcome any that you already have with your dog.
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. 
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