My father-in-law and I ran a month-long family & friends coyote hunting contest this year. It was pretty much limited to our families, neighbors, and their partner of choice (if they had another friend they wanted to hunt with instead of their kid or whoever) and was done for fun and some prize money. It all went pretty well, except we ended up with some issues from the partner of choice thing.
Our rules simply were take a picture of the downed dog and send it to us. We had them keep tails for a longest tail prize. Everyone was fine, except two people. One was caught by one of our cousins picking up a roadkill coyote. He got punked out and didn't turn it in. Another, who I've since heard plenty of stories about, supposedly had asked some other hunters for their coyotes so he could turn them in. He texted me claiming kills but wouldn't send a picture until a week later. His tail won the longest tail prize, but who knows if it was really from a yote that he killed. He also told me that he spent a lot of time road hunting.
We'd like to make some changes next year, but still keep it fun and relatively hassle-free. First change is that we'll make sure some people aren't invited. We've considered having them bring them to my house to check them in, take a picture at the point of kill with some type of object/tag/wooden block that we issue out at the start of the contest with said item in the picture, cut off an ear or something and bring it in. I'm afraid they'll still have ways around it. Any suggestions?