I'm having terrible trouble with a cat problem. A really mangy looking ginger Tom (no reference to Nao

) has moved into my back garden, it turned up about a month ago, and is terrorizing my beautiful little girl.

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old pic- she's few months older now, but, awww, looks cute in this.
He regularly attacks her to the point where she is now too frightened to go in the garden without me - which is difficult when i'm at work all day. She's reverted to using a 'dirtbox' which she hasn't needed since she was a kitten.
I've tried squirting water over the tom, shouting at it, clapping my hands and 'pst' ing at it, lol, nothing works and it's not catchable, it's not particularly scared of me, it sits just out of reach staring at me.
Any suggestions welcome. It's driving me mad!
P.s Don't think it's a sex issue, mine has been done and it doesn't try to mate her anyway - just savagely attacks.