Yeah I thought about that, and it is thick in most places I hunt. One of the sites suggested a long lead and a harness, much like the the K9 drug dogs work. My Lab would pull like a mule and that lead would get hung in everything.
What I think I will do is put a bell on him. He will hear the bell and, hopefully, think .."this is work, not play, we are searching for blood/deer".
And I will hear the bell as he works. In daylight he can probably work loose. Maybe, I'll be learning too.