Hi I live in a first floor flat with internal stairs that are for our own use. We have 2 cats male and female (both neutered). We have cat flaps on 2 doors top and bottom of the stairs. Now the problem is that another cat/cats are coming in at night and peeing at the top and bottom.I think it is prob coming in and eating the food too but no smell in the house. The cat flap at the bottom of the stairs is magnetic but I'm guessing the rogue cat also has a magnet collar. So is there anything we can do to stop this? Can't afford to put in an infa red (I think thats right) cat flap. The smell is horrible.