Cat stressed

I have 2 female cats (mother and daughter), and next door's male cat is very interested in them. They are all neutered, so no worries in that department, but one of my cats is evry timid, and the boy cat has just started coming in the cat flap which casues her distress. Is there an odour that will deter male cats only? I have tried to deter him with a water pistol but he is very persistent and keeps coming back!

Answer by Kate
No i have not come across a odour that will deter only male cats. Is it possible to change the cat flap to one that can only be opened by a specail collar on your cat?
Apart from actaully preventing access to the house like this i don't know what else can be done, as you say male cats can be very persistent and any cat deterents will also affect your cats i'm afraid.

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