locking capabilities is clearly on my PM wish list !.
What I've done, as a workarround, when intensive work needs to be done on PM 'on top of placed drawings' (ie, lots of revision markers/bubbles on window schedules, etc.), is to temporarily copy and paste onto the Master sheet, so the PMK drawing looks 'ghosted' on yr worksheet. Then you can work on it without ever selecting the PMK by mistake.
If you plan ahead, a Master sheet can be set-up in advance for the team, for this purpose. Hope this helps.