I'm gonna' get laughed at here, but I use the little plastic squeakers that go in dog toys and stuffed animals. I put it under the toe of my boot and just squeak it softly every now and then. It doesn't sound like any kind of animal in particular, but varmints are very curious and more than a few coyotes and bobcats have come to see what's making that durn noise. I buy them at craft stores or on-line for like $3.50/dozen and one will last a couple dozen hunts before the seam splits. They will usually stop a moving deer long enough for a shot, too, and using it under your boot leaves both hands free.
"I have no idea what WW-III will be fought with, but WW-IV will be fought with sticks and stones."