One of the best tools I have (and there are many!) is known as a Tripe Knife. It looks like a boning knife with a blunt 'bullet' tip, and is sharp on the inside curve i.e the shortest side. The one I have is made by F.Dick of Germany, but this one is similar:
The bullet tip pushes with ease between the skin and flesh without damaging either, and the blade then slices open the skin effortlessly. It's a bit like a gut hook that actually works and never gets clogged with hair! It opens up leg skin so quickly it has to be seen to be believed!!