A domestic cat. The more and louder it howls, the better it works. I've used one in a wire cage on several occasions with great success. As usual, coyotes come in first but bobcats seem to come in nearly as fast plus be much less cautious.
Failing that, I use some liquid fish oil as an attractant. That stuff is pretty cheap at the drug store and it seems everything is attracted to it. I've had least weasels to bears show up to lick, roll, or just sniff where I've poured some on the ground. Other products may work better but one cannot beat the price of fish oil.
