Quick question - after some help with the K10D for use in panaramas.

In manual mode - how do I lock focus? I have found 3 ways, neither overly satisfactory

1) try to keep shutter half pressed --- very tricky

2) try to keep AF button pressed --- quite tricky when holding camera in portrait and trying to hold steady and pan properly

3) half press to AF then switch to MF --- tends to lose focus as you brush the lens barrel. (The focus rings lenses i'm using at least - Sigmas - are very loose when in MF mode.)

Is there another way?