that it creates a boundary but not look like a fence. Place 2 or three on you property. line spaced at regular intervals. if pickets cannot be placed I would create an imaginary border with a few rocks on boulders and plant around them. A nice manicured and clean lawn, flower beds at your property will discourage kids from playing on or near them and it gives you a good enough reason to complain to their parents if they stomp around your lawn, plants and flowers.