How to prevent visitors from touching your system

I’ve had two instances of “hi-fi invasion”.
 

In the first case, a visitor mindlessly set a bunch of heavy stuff on top of my turntable, deeply scratching the plexiglas dust cover.  
 

Another time, during a family get-together, I was away for a few hours to pick up some groceries.  When I returned, my 20-something nephew commented how great my tube stereo sounded.  He had taken it upon himself to turn everything on (and it was a complicated high value multi-component system) to play music for the crowd!  No damage, I suppose, but it left me feeling invaded.

With so more kindness i only can say thanks...

And wish more than only my best for you...

@mahgister So happy you are back. I appreciate you.  

Everyone I know does not touch, they may look and admire. I believe they respect the fact that it is not theirs, so no touchie touchie....

Friends to touch my audio gear, who needs friends when I have records to fondle er ah play. Aaaaaahhhhhh vinyl.

No, no, no, is that a Scratch what to do, what to do, no,no,no,no.

Records to die for, equipment to touch.