Ground black pepper seems to work well for repelling mammalian pests. Another option is using those small 1-3 foot fences.
I personally believe that cats should be alowed to go outside because they are then enabled to get fresh air, frolick in the open, hunt and do all the things that are inherent in the instincts of the species. So, even though it is often advertized that it is healthier for people to keep their cats inside, I personally believe that it is healthier to allow the cat to go outside.
Of course, the flip side of the coin is that cats reek havoc on local bird populations in some areas and in certain countries and areas it has been necessary to disallow cats from being kept outside.