Where are you getting the PCBs made, most manufacturers will, even for batches of many PCBs, depanelise for you at their end.
If you do get a PCB attached to a panel, my advice for removal would be to use a "sharp D" profiled needle file (flat on one side, curve on the other, fairly sharp edges at the top and bottom of this D shape) as you would a hacksaw, using a file instead as you can be a bit more delicate filing with the sharp edge than you can sawing by hacksaw. This will get through PCB material pretty quickly and give a clean edge without causing any violent stresses elsewhere on the board. Make sure the board id designed so there is no copper of any layer close to the area you are filing through, as filing in to a copper area could cause tears which could spread elsewhere on the board.