Once an instrument is where you want it, select it and click Lock in the tool row. A locked instrument does not move when dragged, aligned or nudged, so you cannot knock it out of place while working on the rest of the panel.
Lock works on several selected instruments at once and on a group.
To move a locked instrument again, select it and click Unlock. Lock and Unlock leave the instrument selected, so you can press one straight after the other.