Dude... just buy a shit-load of salt, when I say shit-load I mean... Like 9 or 10 huge economy size tubs of it. And just pour it all over there yard, and make sure it's good and saturated. Get creative, try to write things really big in their yard like "Crack house" or my personal favorite "Homo House". But pour salt on everything that grows in theer yard. Grass, flowers, bushes, everything. Oh... and get plastic forks and stick the prongs in the ground and break off the handle... do that all over the yard.