Just Disappear them mate taken em to the local council pound or to the rspca say that you kept finding these cats killing natives in your yard and you want them inpounded !! if there not registered if the owners go looking for them they will cop a good fine and have to pay them for release !! slowly one by one disappear them all till theres none left at all !!! and when they come looking for them act dumb !!!! ( i didnt even know you owned cats ). at the end of the day if there on your property and causing damage then get rid of them !!! Chinese Chicken - hmmmmmmmmmmmmmm Yummmmmmm !