I had big problems with my youngest cat when I got Holly. He actually attacked her a couple of times in the garden. What I did was to throw water on him--he soon realised that that was a no go. Inside I used a spray bottle. within 4 weeks or so they were good friends and now play and sleep together. He is about 6 times the size of tiny Holly, but now sheaths his claws when they play. If I can see he is irritated, I distract her with a toy, walk etc. to give him some peace. Good luck.
__________________  Sandra J and Holly  |