In the canine world, scent marking is an important means of communication, and when a new individual is acquired, there may be an apparent breakdown in the toilet training of the established dog. In reality, however, this tends to be related to the stress induced by the intrusion of the newcomer. This situation is worse in the case of male dogs. This is because they have a higher level of the male sex hormone, called testosterone, in their circulation, which serves, amongst other functions, to stimulate territorial marking with urine.
Perhaps not surprisingly, such behaviour is unlikely to become apparent much before puberty, and peaks in young dogs between their second and third year. This phase should pass as the order of dominance is reasserted, but if it persists, then rather than punish the dog for what is a natural reaction to an incursion on to its territory, you should discuss the problem with your vet. Castration of both dogs can be advisable under these circumstances. This will certainly reduce the level of soiling indoors, and hopefully eliminate it entirely in these surroundings.
For a shorter-term option, however, the use of a progesterone-type drug may resolve the problem, allowing the dogs to become better acquainted in this time. If you catch the dog spraying indoors, you can treat it as outlined earlier with regard to toilet training, but it is most unwise to react at a later stage. This will be perceived as a further attack on its status, and the cause will not be appreciated, and consequently the situation can inadvertently be worsened.
There can be times when dogs, either living in groups or on their own, may become more aggressive or excitable than normal. This often occurs before a thunderstorm. Dogs arc able to detect the sounds of the storm before these are audible to our cars, and will become scared. In severe cases, you may need to obtain sedatives from your vet, especially if you live in an area where thunderstorms arc a fairly regular occurrence. Alternatively you may want to try to desensitize your dogs by recording the noise of a storm, and then playing this back to them. Start at a low volume, giving plenty of encouragement, and provided that the dogs do not become distressed, you can increase the volume somewhat. Repetition and making a fuss of your pets, effectively distracting their attention at first if they start to become nervous, should overcome the problem over a period. Time spent on this activity will not be wasted, especially if you have the misfortune to be caught out in a storm with the dogs. The last thing which you will want at this stage is for them to run off in opposite directions through fear.
You will need to feed the dogs separately, to avoid possible conflict over food. The garden can be useful for this purpose, as it is easy to separate the dogs without any risk of aggression at mealtimes.