Last season I have tried him on man made fox burrows, but he was a little too big for the plastic pipe.
He tried to destroy the pipe, but didn't enter it. Only for a body length. On the same day he caught one above and scotched it in a few seconds.
Three weeks ago he entered a natural burrow, but the fox escaped (too many entrances, some very hidden).
I think he lacks nose. He scent the fox in the burrow, but not much better like I do.
He is a strong finisher, so I will test him next season on badger.
He works very good on wild boar and is able to work in a pack, even with stranger dogs.