Have just completed a total rip out of a 100 year old mud job bathroom. Have replaced lead trap and all 4inch cast waste line with 4 inch pvc. Question how to protect the pvc in the wall before I rock it up

Protect from what? Use nail guards.

protect from what? use nail guards.
Thanks for your interest, yes nail guards sounds good do they come in 16 inch wide x 8feet high. I have replaced all the old 4 inch cast with pvc from basement to 3rd flloor and need to protect it.

I don't think you've got that much to worry about. Your sheet rock is nailed, better screwed, to the studs and the pipe runs parallel to the studs. You only need to protect the pipe if you do a 90 through the stud and you can't do that with a 4" pvc.