Is there any practice or products out there to help protect a PVC pipe where someone might drill into the wall in the future for hanging stuff or something. I'm considering just using metal piping for my vertical vent pipe runs through the walls.
I believe that code requires it to be located at least 1-1/2 inches from the wall (or framing?) face or to be covered by at least 1/16" steel plates (similar to wiring, and for the same reason.) This is why (as implied in @John Gaughan's comment) wet walls are typically framed with 2x6 or even 2x8 rather than 2x4 lumber (that would be a "practice" in the spirit of your question.) Another method is to use 2 separated rows of 2x3 or 2x4 framing, which saves on a lot of hole drilling and lumber cost. Does not prevent the determined idiot from finding a pipe and drilling something longer than code expects into it, but nothing does, really.
On the whole, I prefer PVC - having dealt with corroded metal pipes (those can be drilled through as well.) Providing an actual pipe chase (boxed in, rather than trying to "bury it all in the wall") provides more protection (you can give them more space) and should help keep anyone with the slightest clue from drilling there by accident (because it's obviously a pipe chase.) Plus, you don't need to make the rest of the wall excessively thick.