Ivor, i had a similar problem for a couple of years. i live in an inner city community with a large open garden. a neighbouring virile, jaunty and maurauding cat was a very unwelcome visitor to a couple of cats ocver this side of the garden.
a water pistol or a water sprinkler are too polite. What your friend needs is about a good bucket or two of water, full and ready in advance. The Burmese will get the message pretty quickly.