I use hot glue. Just use a crapload of it and you MIGHT have to do maintainance every month or few. Depends on how bad your rats chew, and if you have big chewers, either you need to teach them not to do that or cull them.
Oh, and it doesn't really matter if it's inside or out with BAD chewers. I had some stupidass rats that would chew on the actual wire. Needless to say, I killed them right away. You hear that noise throughout the house. THE. WHOLE. HOUSE.