You could build a cat-run with access from the house - that will help to keep them IN for a first few weeks and who knows - they might get used to it.

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"Do not meddle in the affairs of cats, for they are subtle and will pee on your computer." --Bruce Graham
There are no rules, rules are only for people who fit inside a box, if you want to think out of the box there is no hope... Life has no Box. (Tony Howells)