If you want to trip the shutter without locking it open, a screw-lock cable works great.
If you want to lock it open, an auto lock works great, holds reliably, and minimizes the chance of moving the camera. Just be in the habit of having it set for the way you want it to operate before the exposure (like checking that the lens cap is off), or it will lock (or not) when you don't (or do) want it to, over and over, in which case you might hate it.