If a cat is peeing anywhere outside the litterbox and it's been spayed/neutered, there's a problem that you have to figure out - it doesn't like the brand of litter you're using, the litterbox isn't scooped/cleaned often enough, litterbox is in the wrong place, there's another animal in the house that's preventing it from using the box (or it doesn't like sharing a box with another cat), etc. It could even be that it's marking its territory if it knows there are other/stray cats that are coming around outside. It's a process to figure out why a cat is peeing in places other than the litterbox but it's not impossible. Good luck!