OK. I have 8 of the little devils - all strays that I've reluctantly taken in because I am a push over when it comes to cats. I use old, rusty stock fencing. If you go out into the countryside you will often see bundles/roles of it discarded next to new fences that have been replaced. The farmer or shepherds will only be too glad for you to take it away as long as you ask permission.
'Rusty' fencing is best because you can't see it against the colour of the earth - it is quite invisible from even a few feet away, especially once the plants start growing. 'Old' fencing is best because it is most effective if it is crumpled up befor it is laid over the top. If the fencing is too flat, the cats will just scratch in between the wires, eventually covering them with soil, so your barrier will vanish! If it is well crinkled up it is much more difficult for the cats to wiggle their paws and bums in around in it. I have had no problems with them getting stuck or anything like that because stock fencing (unlike more dence guage fencing) has quite wide square gaps. A double layer put over the vegitables and flowers is even more effective, but the more layers, the more difficult it is to lift and to weed, so a good ballence depends on the crop/flower type.