If you're using a genuine ford one or payen and they keep going there's definately something wrong.....as said get the block tested for starters. I've never had a headgasket failiure in 6 years of owning mine and several different engine guises so i'd say (even though you don't want to hear it), you're either doing something wrong or you have a problem with the head/block as the gaskets are generally very reliable!