I fear you've opened a can of worms here, McGrath.

Whilst George Bernard Shaw famously once said that"England and America are two countries divided by a common language" we are perhaps even more divided on the issue of letting cats outside.

Simply put Amercans tend to favour indoor only, the British prefer to let them roam. A quick google search will provide you with more on the issue than you could ever hope to read.

Back to your original question, you've got no chance of persuading them to stay in your garden. Set them free and let them take their chances. Better a life lived well than a long one.

But then I am English...