Assuming your fence is privacy fence How about taking a cheaper method and building a second fence made of chicken wire or hardware cloth on the top of the fence build it using your posts as support and building a protruding frame heading out. think of a chain link fence with barbwire you know how the barbwire supprt beams angle out. well this creates a block so that even if a predetor could reach the top of the wood there face would smack into it and unless it can manage to turn itself like spiderman and crawl upside down. (chicken wire wouldnt support its weight) it wouldnt be able to get in. since i seem to have confused myself I can send you pictures of what I mean if need be.