This is whats going on:
My principal (cliënt if you will) always receives the drawings on paper (by old fashioned postman) and also digital as *.pdf. Some of them ask for *.dwg and I have no problem with that.
But, I know there are a few amongst them that keep asking for the *.dwg version of whatever I make. ...
... but in some cases I would like to say NO, I will not send you the *.dwg. ... But since I am no boss around here, and it is still the cliënt...
Here's my two cents, for what it's worth.
First, I agree with Alan (alanjt) in regards to who is paying the bill. If the 'client' has in the contract to receive *.dwg's, then as the others have mentioned, it is probably best to send them the *.dwg's.
On the other hand, if there is no agreement in the contract, and they call you or ask over an email, tell them there are proprietary elements in the drawing that constitute copyright infringement if you send them the drawings.
Talk it over with your Boss. Let him/them know you are uncomfortable sending out the office's proprietary information.
Lastly, if you really need to sabotage a drawing, write a simple LiSP that will delete (or just make invisible) all of the blocks and leave in the blocks place a text line that says "Proprietary".
I would prefer invisible, then have another LiSP that will make them visible again so you can continue to use the drawing. Of course there is the risk of "them" figuring that part out.