We have always had a cat flap, and because Reggie was so small he would go through it all the time, but the cat broke the flap when he was chased in by another cat, so we decided as Reg was using the flap anyway to get a bigger sturdier dog flap. Reggie and the cat go through it happily, and we tried putting Archie through it, he went out ok, then came back with help again, so we gave him a treat. However when we tried again, Archie then attacked Reggie quite fiercely, and they had to be pulled apart.
Is there anyway other than seperating them that we can teach Archie to go through the flap? Any ideas would be welcome pls?