Meowy Catkin
Meow!
My friends built-like-a-brick-*****house welsh sec D used to bolt off in random directions when led. They were told to try a chiffney and the horse leads like a lamb in it. Do try one just incase it works for your neddy too. 
Try Kemp Controller-Its bloomin FABHi all, hope someone may be able to offer 'the lightbulb' help we need.
We have 16.2 IDx tank-like gelding who is becoming a real nuisance to lead in from the field.
We able to approach and catch him, he will walk with you like a little lamb lulling you into a false sense of security and then without warning he will turn to the right and run, he dosen't rear or strike out he just literally turns on a sixpence (which is amazing given the size of him) there is nothing you can do to stop him.
We have tried the following:
1. leading in a bridle - snapped the reins.
2. leading in a Dually & leadrope - still couldn't hold him leadrope dangling as he runs & got caught in his shoe/hoof.
3. leading in a Dually & 12ft line - still couldn't hold him 12ft line wrapped round his legs which was awful to watch as he just kept falling over.
4. leading in a Be Nice / headcollar with poll pressure - still couldn't hold him.
Because he is so strong the leadrope / 12ft line just goes through your fingers, nice rope burns if you don't have gloves on.
He is fine to lead round the yard and will do groundwork exercises in the menage backing up, turn on the forehand etc till the cows come home, he knows exactly what he is doing and to be honest knows his own strength, myself & my daughter are just no match for him, even my OH could not hold him.
Any suggestions at all - other than bloody hobbling him (just joking)......