Cats keep pooping in our back garden ?

We have a gazebo in our back garden and these 2 cats keep going and pooping in it and burying it with the stones in the gazebo. There destroying the plastic under the stones and our garden STINKS. Iv complained to the owner of the cats but they still keep coming like 5 times a day or whatever. Is there something we can put in the garden 2 scare them away?? Someone said bottles of water but I dont get how that works anyways thanks x