i don't have much experience of taking fox with running dogs, think I've only had about half a dozen, all taken by a straight whippet, who even at 19 1/2inches and 26 pound , must outweigh the majority of foxes( what is the average weigh of an adult fox anyway ?) and therefore had the physical advantages, even a couple of pound would make a big difference , he seemed to have a knack for pinning them with a throat hold and not getting bitten, now I'm obviously not advocating whippets or whippets crosses as regular fox dogs but they can and do take them. how big does a dog have to be to take fox