What can i do if my neighbour refuses to clean up all the cat poo from his

[Gary]

garden? It stinks!!! Help Please? My next door neighbour has got about 14 cats and not only do they use my garden as their toilet, they also use his. They also sometimes feel the need to go on the top of his porch roof!!! (Nice I know) Now i have come to terms that i will have to clean their mess up from my garden, but what can i do about his garden??? As you can imagine when the warmer weather comes it will be unbearable... Any suggestions would be welcomed