Very true! The best way to convince an unfriendly cat that you have no intention of invading is to look it dead in the eye, blink a couple of times, and then ignore it completely for the rest of your stay. This says, in cat-language, "Faugh. I could not care less about you and your territory."

If you want to drive them off, it works better if you speak cat. ^^;; Stare intently at the cat you want gone and make that low 'wrrrrrr' noise cats make when they're seriously peeved. Most domestic cats will fuck off, not wanting to get into a fight with someone as big as their owner, and the ones that don't will shortly convince their owners to boot them into the utilities room for the duration of your visit. Problem solved! Now to get rid of the cat dander on the sofa pillows...