Gary-
The herring brine that HBP and craig harr are describing is awesome. The recipe that I use is slighty differnt from theirs though...

1 part rock salt to 1 powdered milk to 1 part borax. I usually fill up a small tupaware container with water and a couple dozen frozen herring (the day before) and use about 1 cup or so of each ingredident.

I have seen some pretty soft ugly bait harden up and start flashing like you would not believe.