Expect confusion and mistakes in the first few days, even in a trained dog. It is vital to use a crate and/or a confinement area so as to not allow opportunities for accidents in the first week or two - this also helps chew-training efforts.
Set your dog up to succeed. If using a crate (highly recommended) it should be just large enough for dog to turn around in and stretch out. If using a confinement area, confine to one uncarpeted room with petproof gates. You can always relax the regime later, but it is very tough to start relaxed and then try to tighten up if there's a problem.
Provide extra opportunities to eliminate outside: First thing in the morning, after eating, every 2 - 3 hours, and last thing before bed.
If your dog doesn't eliminate on any particular outing, try again an hour later. Accompany your dog to eliminate - go with him rather than sending him so that you know whether he's gone or not. You can reward at the right instant - give praise and small food treat as he finishes. Go to the same spot to make it easier, or at least the same kind of surface. Praise and reward all outdoor elimination for the first few days - later you can slack off (it's okay to continue praising.)
Interrupt him ("Ah! Ah! Let's go outside!") at the start of any mistakes indoors, then hustle him outside to finish. If he finishes outside, praise and reward this.
Note: interrupt, not punish. Punishment is not a good idea in early relationship with a new dog, and of dubious value at any time. Even more importantly, if the dog makes a mistake unsupervised, never, ever punish - there is zero connection to the act that happened earlier.
Clean all accidents thoroughly with a commercial odour neutralizer (enzymatic) or 50% vinegar to water. Normal cleaners will not get rid of the smell for your dog. If there is any trace of a smell he may return to the same spot to 'go' again.
- Add one extra room of the house at a time, every few days if the dog is successful.
- Supervise closely every time a room is added.
- Gradually extend the duration between opportunities, adding a half hour per week.
It is reasonable to expect an adult dog to hold on 4 - 5 hours max. Of course, many dogs can hold on longer but is it humane to make them.
Sudden onset of indoor elimination in a trained dog may indicate a medical problem - consult your veterinarian immediately before getting behavior help.
Be Patient! Don't lose your cool. Most dogs will have accidents in the beginning.
Note: Submissive urination is not a house training issue. Dogs/puppies can urinate a small amount with fear and excitement or to please you by showing submissiveness. You can tell the difference between submissive urination and regular housebreaking issues by the amount and circumstances in which it occurs. As the dog gets accustomed to his/her environment this should stop. Do not reprimand your dog for doing this. It could actually increase the behaviour.