Start as housemates, not instant friends
A foster dog arriving for a few weeks is a guest in your dog's territory, carrying unfamiliar smells and an unknown history with food, beds and attention. Aim for polite coexistence, not a bond. Meet away from home first, walking in parallel at a distance where both dogs can notice each other without pulling or fixating, then shorten the gap only as both stay loose and relaxed. At home, begin with the foster in a separate room or behind a gate where they can smell and hear each other without direct access. Let your resident dog keep her usual rooms and privileges; a foster stay that costs her the sofa, her bed spot and your attention all at once is a common recipe for resentment.
Remove everything worth arguing about
Most friction between temporary housemates is about resources, so take resources out of shared space. Feed in separate rooms with doors shut, pick up bowls afterwards, and give chews, stuffed toys and high-value treats only when the dogs are apart. Keep two sets of toys for shared play, choose sturdy ones neither dog guards, and end play while it is still cheerful, before tiredness and arousal tip it over. Manage tight spaces — hallways, doorways, the gap beside the food cupboard — where dogs are forced close together, and do not let them crowd you at the door or compete for greetings when people come home. Separate them completely when nobody is home, however well the supervised hours have gone.
Run two routines side by side
Peace is easier when both dogs are properly exercised, fed and rested, because a bored or overtired dog starts trouble. Walk them separately at first so each gets training and sniffing time at their own level, adding joint walks once parallel time outdoors is relaxed. Keep rest sacred: foster dogs in particular often need far more sleep than they will take in a busy shared room, so build enforced crate or room rest into the day. Rotate who is out with the family in the evening if full togetherness is still a work in progress, so neither dog spends the whole stay exiled. Tell the rescue or fostering contact promptly about guarding, scuffles or a dog who cannot settle, since they may adjust the placement or offer behaviour support.
End shared time before it goes wrong
Learn each dog's early warnings and act on the small ones: a hard stare, freezing over a toy, body-blocking you or a doorway, or one dog persistently following and pestering the other. Interrupt calmly, separate, and give both something quiet to do apart; do not punish growling, which is information you need. Any actual fight, bite, or a pattern of one dog hiding, losing appetite or refusing to come into shared rooms means the arrangement needs outside help the same week — speak to the fostering organisation and your vet rather than persevering for the remaining weeks. KinsLe Care Teams keeps the two dogs' feeds, walks, rest breaks and settle duties listed separately with each task marked done, so a busy household can prove at a glance that both dogs got everything, even on the most chaotic foster day.