There seem to be overlapping issues in this request. Cats, foxes and hedgehogs, and slugs. Is the cat coming and going in the house as she is supposed to, or are other animals coming through the cat door? Were the other critters a problem in your garden, or just the slugs?

A caller to a local organic gardening program had a suggestion that I'm trying now that may help some aspect of this.

Take a two-liter bottle and at a line just below the "shoulder" of the bottle, make a neat straight cut through so that the top is a sort of funnel and can be turned over and pushed narrow end down into the base. You tape the raw edges where they meet and end up with a bottle that has a narrow opening to the inside that slugs or snails crawl through but can't get back out very easily. Push some pieces of bread and a little water in to make it moist to smell interesting and you'll lure garden pests in and can untape and toss bottle contents in the compost later. What I usually do for snails and slugs is to put out a shallow container (like a restaurant take-out 1/4 pound plastic container) of beer and they find their way in and drown in it.

If you feed the foxes and such they will keep coming back for more. They may bother or eat the cats.

SRS