What's your run made out of? I can tell you that my chain-link kennel is very secure for larger predators (skunk or bigger) but mink are a risk here at night and they only need a quarter-sized hole to get in. I can also tell you that I see physical evidence that predators have attempted to get in -- bent wires in places. So, unless your run is made of hardware cloth, you should start training them to sleep indoors and shut the door or it's only a matter of time.