And although I haven't met him, sounds like fairly extreme lead problems atm.
This is an 8mo old Weimeraner cross, rehomed about 2 weeks ago. He is lovely natured, clever, and has started to settle well....but my friend is tearing her hair out over how to walk him safely as he just can't cope with leads. As soon as he is on one (they are using a harness at the moment), he tears around in circles in a complete panic, and lies flat to wriggle out of the harness.
His owner thinks maybe he was left tied up outside for hours in his former life 
Off lead, he's a bit manic but pretty well behaved - but as they're in London, getting him to a common or park without using a lead is nigh on impossible. They've tried all sorts of ways to get him used to the lead, playing with it, putting him on it at home and walking around...but not made any difference so far. They haven't tried a halti yet, but are wondering if it might help?
They are reasonably experienced dog owners, very committed and wanting to help their boy settle down...but they haven't come across this before, and probably don't have much money for trainers.
I have absolutely NO experience with this kind of thing - any help, tips, or ideas as to who to talk to very welcome!