How to hide screen when logged into remote iMac
Awhile back, I discovered an even better, simpler, more reliable, and free way to accomplish the goal of screen sharing without people being able to mess with the remote mac or observe you working.  All you have to do is:


Create a secondary user on the remote mac.
Screen share into your account (assuming it's the one that has the screen locked).
Use fast user switching to switch accounts to the secondary account
Lock the screen of the remote mac using the apple menu -> "Lock Screen" option
End the screen sharing session
Screen share into your account again (which no longer is showing on the screen of the remote mac).


Viola!  You can now work without anyone messing with your keyboard or watching what you're doing.  Much more reliable of a method than Shades and free too.