Homebrew PCBs

I'm often finding that my toner transfer boards are ALMOST usable, but have a few trace breaks that need to be touched up by hand before etching.

I've seen it said several places that ordinary Sharpie markers make suitable resist-ink for this purpose (I actually remember buying an old Radio Shack home PCB kit that came with a Sharpie and called it a "resist ink pen").

I recently tried this using a Sharpie-brand "ultra fine-point, super-permanent ink" pen, but the FeCl ate right thought the ink.  

Has anybody had lucks using Sharpies as resist-ink?  Are there any recommendations on something better?