I have approximaltely a one acre back yard, and need to rid it of fleas inexpensively. But it must be safe for my dog to be able to be out in it. I am treating the dog and my cats. Also treating the house. But must figure out how to eliminate them out of the huge backyard I have where my dog frequently plays. Does anyone have any suggestions of what I can do to cure this problem. ANY HELP would be greatly appreciated. Desperate!!!!!!