Keeping Neighbor's Cats Away?

I have two neighbors that love leaving their cats and kittens outside all the time. If they are not meowing the cats are peeing on my windows, doors, anywhere they can. I try to be a responsible pet owner and keep my cat inside or on a leash like our dog when they are outside. I've tried several powders and sprays to keep them away and so far nothing seems to work.

Now because of the outside cats/kittens my cat is starting to pee everywhere. I don't know what else to do. I am at my wits end and I don't want to have to get rid of my cat because of other pet owners and their carelessness. Please I would love some advice on what I can try or do to fix this problem. I would try the motion sensor water sprinkler, but being in an apartment complex we have none, at least ours doesn't. Please help!