Every time your dog pees or poops outside it needs to be celebrated. Give them baby talk or a treat, jump up & down, pat their little heads & remind them of how brilliant that decision was. Yes it might look silly, but your pup needs to know he’s done the best thing ever. When you consistently praise your puppy for going potty outside they’ll start to understand that it’s the correct decision, and one that leads to super fun happy time.
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.
Many owners appear disappointed that their young puppy will not toilet when out on a walk, yet relieves itself the second it gets back home. This is because the puppy has been taught to toilet only at home (hopefully in its garden), and being creatures of habit, they often wait until they have returned home before evacuating their bladder and/ or bowels.