Thanks to everybody for the input. The more I try to sort out what would work best for us the more it sounds like texturing is the answer. I guess we just cough up the dough for the embossing machine and put texture on any proofs we sell or send out. I don't think just putting the studio name on the proofs will deter people enough.
I was also talking to a guy at one of the labs we use today who mentioned something about a paper that's out there which only shows the PROOF watermark if somebody tries to copy or scan the image. 1st time I've ever heard of it but if it works and isn't cost prohibitive it could solve the problem.
BTW,
here's the link to the texturing machine I'm looking at if anybody is interested.