I have a system I use in Whitetail hunting during the rut that seems to work for me. When I make a mock scrape in the area I wish to hunt I will place a couple of 35mm film canisters (film removed of course) in the scrape after I have cleared out all leaves and other debris. The film canisters are filled with cotton balls and saturated with doe in heat urine. This keeps the urine from soaking in the ground and can be refreshed on each trip if needed.