I personaly prefer not tu use more than a dog in a dig, but here in spain when you hunt in Pipelines of irrigation or in batteries of straw could use 2 dogs (not underground because underground there is only place for one fighting with the fox)
You could look for smaller jagds because hunting is one thing and digging another. Some jagds are quite big for working fox in dig (better for wild boar ...) but you could find someones of arround 33 cm
When a terrier kills the fox in the dig its difficult that he could take it out, probably you should have to dig but another dog is not going to he
