I use the steering lock, a disc lock and insurance. Thats it. I'm 5' 7" so when I stand next to the bike it looks massive. Most people are intimidated by their size so I'm hoping that's deterrent enough. Without the key it's useless anyway and so I only have to worry about kids. It was parked outside my brothers recently and some kids pissed on it.
I have to give them extra points for having such a high aim. One bucket of water later I was on the road. I guess they figured if they couldn't wheel it away they would spoil it.