Getting rid of a tomcat without harassing our cat?

[SidewinderINC]

I know there's a good few cat owners on here so might have better luck than a google search

We've just moved into our new place and Richard has a little lady cat who's getting on fine and is now venturing outside. The downside to this is there's an evil tomcat around the area that keeps wazzing up everything in the garden now and it's really putting her off.

Does anyone know of a way of keeping the tomcat out, whilst not putting her off going outside herself?

The logical option is buy a tube of tennis balls and keep him out the old fashioned way, but not really keen on that.