Steve Walker wrote:

Get a new cat flap .One that locks .

It does, but the cat simply breaks it open like a dawn raid by the
Sweeney...

Judging by the number of cats in this thread who are perfectly capable
of reducing a catflap to scrap plastic in a matter of minutes (and I
thought it was just ours!) I do wonder why some manufacturer hasn't come
up with a decent 'heavy duty' model, "for the more assertive pet..."

David