I've now obtained the ingredients from the butcher - I suspect that there should be something liquid in the list. Here is what they put in their marinade: onion, shallot, chives, dill, parsley, tarragon, rosemary, pepper, salt.
I'm guessing they'd use a vinegar of some kind and an olive oil. I'll return there and find out what they useand the quantities. It is good in the mouth!