Years back, I killed dozens of grey foxes with an electronic game caller...The best producer was a recording of a grey fox pup in distress.. The sqealing rabbit works well too..

I used a shotgun with #4 shot and it killed well out to 40 or 45 yards...

A 3 inch mag with turkey loads would work fine...

A .22 LR with hollow points also works well and will anchor a fox with most any solid torso hit... It's more "fur freindly" than centerfires...

The .17 HMR did not exist when I was fox hunting, but I suspect it would be a good choice, also..