Great idea Merlins Mum !!
One of my cats is semi feral and an expert at getting out of his collar.
He has to wear a bell however to lessen the amount of 'presents' he brings home for us.
I buy cheap collars of ebay at the moment and keep lots of them in, they generally only last a week if that
The one he has on now seems to have done well however, he has 4 bells attached to it so you can hear him coming a mile off!