Tough one then, might have to be the chipped collars though a friend of mine once said they were not that good. And as you know with parrots, where there's a will, there's a way! Maybe a porch on the outside door. If parrot gets through one door, you might just be able to catch them before they reach the other cat flap! Is your bird scared of anything? My Ruby hates rope perches so I hang them on no-go areas. Looks odd on the TV but does act as a deterrent.