The indoor territory should only be available to the resident cat. To avoid problems of other cats entering the home, which can cause [[Indoor Marking - Cat|urine spraying]] or [[Feline Aggression Towards Other Cats in the Same Household|aggression between the resident cats]], it is best to fit an electronic cat flap with personalised coded collar keys that allow only the selected cats to enter. | The indoor territory should only be available to the resident cat. To avoid problems of other cats entering the home, which can cause [[Indoor Marking - Cat|urine spraying]] or [[Feline Aggression Towards Other Cats in the Same Household|aggression between the resident cats]], it is best to fit an electronic cat flap with personalised coded collar keys that allow only the selected cats to enter. |