They don't evan bury it,i'm sure i remember that cats usually like covering it up---my neighbour has got 14 cats though don't know if they are stressed re territorial issues -by the way i love cats

You could buy river rock or crushed brick and place a layer of it all in the garden where there isn't a plant you want, this would also discourage weeds.

tell her and if they dont stop call the spca

They don't bury it? Try putting out some moth balls. The problem is that your neighbor has 14 cats and often a cat will not want to go in anther cat's space. I doubt she has 14 litter - boxes.