Vile Carwash!!!

Question
Hi Carrisa,
I am in a bit of a pickle at the moment, I recently moved in (roughly 2 months ago) to a friends with my boyfriend and our 2 cats!
The problem is our friend already has a cat which is quite aggressive and at first he would not accept either of our cats into his home but then everything was ok, they seemed to be tolerating each other...that was until about a month ago when we had a cat flap fitted.
Now our friends cat (Carwash) is being aggressive toward our girl cat (Pumpkin-about 2 years old) and I am very worried as she has scratch marks all over her back from him and she is hardly coming back home at all.
Carwash keeps garding the cat flap and whenever he sees Pumpkin he runs after her and hits her. She just keeps rolling onto her back and lying there very submissive but he still doesnt stop.
The only time that she comes in now is to have a little food (which she wolfs down at an alarming rate) and then shes back off outside.
Carwash is only a kitten (hes not even 1 yet) but he has been a very aggressive cat from the start and he often lets you stroke him and then he turns around and bites you or hits you.
I dont know if he is doing this to Pumpkin as a social status thing or if it is because he is not getting the attention the he desires from his owner. Also, I am not sure how receptive our friend will be to re-training his cat-he can be very difficult sometimes (the owner and not the cat...this time-LOl) I am really very worried that Pumpkin will not come back soon and that she will find another owner...we cannot afford to have her chipped at the moment.
The main problem that I am finding is that I can monitor them in the house but I do not know how to punish Carwash and as soon as they are outside I cannot watch them anymore and Carwash is being very aggressive again.
I do hope that all of this makes sense and that you are able to help me with this HUGE problem.
I really am getting very worried as they have been fighting again just...
Thanks so much
Joy

Answer
Hi Joy,

It appears that carwash doesn't like Pumpkin and finds her intolerable at the moment. It can be due to him being terriorial. After all, it's Pumpkin that's intruding into his territory. When Pumpkin lies on her back, Pumpkin is trying to tell Carwash that she wants to be friend to him.

I'm not sure if Carwash and Pumpkin are merely playing or fighting. If there's really injury on Pumpkin, the foremost thing for you to do is to separate the two of them and treat Pumpkin's wound before it gets infected.

Try to keep Pumpkin indoor first, maybe in your room until Pumpkin knows that it is her new home. When you are at home, try to let Carwash and Pumpkin interact under supervision (to ensure that Carwash doesn't 'attack' Pumpkin for at least a few days). For some cats, it may take months before the territorial cat allow another cat into his territory.

Carrisa