I am Carrie!!
Ktreva's ideas are, as usual, excellent. I would also get him to sit and put the leash on him just before you feed him. Get the food ready so he knows what is coming but don't actually give it to him until he has sat quietly while you put the lead on. This may take a little while to accomplish at first but it is worth it.
If you play fetch with him put the lead on for a few seconds and then take it off before you throw the ball, making sure he sits quietly.
Anything you do with him that he enjoys - put the lead on first (take it off after a few seconds). The more you do it while he is concentrating on something enjoyable the easier it will be for him to accept it.
Good luck, let us know how it goes.
I would guess he has been caught or nipped by the clasp of a lead at some point and is wary of it.