I seen it when we were checking a earth the dog wasnt searching for fox just hiding from us would come out when tried grab ran down the nearest hole like a skulking ferret it did this more than one occassion, a complete pain in the ass and massive waist of time, it wasnt even a good terrier surprised the owner kept it!
could you not of just dug the fox out and the dog would of come out for rag, then grab it!