Nervousness

I'm wondering if anyone has any advice for me. We hadn't really taken the dogs out over Christmas as it was too treacherous where we live and also because they didn't want to go out in the cold (the pansies). But recently, when I try to walk Hagrid, he has gotten increasingly nervous and continually wails as you try to walk him. I've given him a good check over and there doesn't seem to be anything wrong with him physically. He has always been of a "nervous disposition" but never had any real issues when walking that couldn't have been overcome. If anyone knows of anything I could try I'd really appreciate it!