If you are lucky enough to have a garden but dislike other people having easy access to it by simply climbing over the fence then there is a cheap easy way to stop both opportunist thief's and nuisance cats.
It's a good idea to check with your local council or police before doing this security measure.
Simply obtain some carpet gripper from your local carpet shop and firstly treat it with wood preserver to prevent it from going rotten. then simply nail it to the top of the fence, carpet gripper has nails already fixed to it, so it is simply a matter of placing it on top of the fence panel and knocking the nails in with a hammer.
This is A great way to stop cats from fouling your garden as well, they normally only try walking along the fence once!
If theft from your garden is an issue then you could try Alarm mines
You could also consider installing a security light -