My old beddy whippet is a decent marker, i just let her hunt about she will find one and mark it. I find her really useful doing big warrens, after a bit of bolting when you think the warren might be clear, i say to her were is it at, she will then go back around the holes and mark if one there, you are then dropping the ferret near hand on top of the rabbit, i just keep repeating until she isnt interested, i think it saves a lot of steam in your ferrets and a lot of time. Just my personal opinion though. I have a young dog i am learning now, i find it best with him to stand well back off the