I don't patch - I replace. However, everybody knows that some patch and some don't, so I'll try adding something of value to the discussion:
If you don't definitively locate the source of a puncture and remove it, you need to accept the possibility that a sharp bit is still stuck in the wheel and may flat you again. Heck, even if you find and remove a shard, there might be more. Every time that happens, I would suggest slapping a dollar bill sized patch around the area to protect your new tube/new patch for awhile - even if the tire looks fine. You can always remove it later. I don't have any great suggestions about what might be the best material to use, but I suppose anything is better than nothing.