If you DON"T have home switches, You can jog to your PART x0,y0 and zero the Part (G54) DRO's and also hit the Ref ALL HOME button. As long as you never hit the Ref ALL HOME again, it will duplicate you PART 0,0, so if you mess up your part coord, you can look at the MACHINE coords and coopy that value into the PART coord DRO and you will be back where you were.
All you really need is a small hole somewhere on your stock just off of the finished surface. Save the coord of that hole so you can pick it up later if you need to. Or, ref. the vise jaw and stop ... if using one.
Other ways too, I'm sure.
Russ