Yep that is the problem. When a cat jumps on a table and you say no she knows why but here to play and to use the claws happens at the same time so........Things should not get worse again. Maybe you will get a better tip or Mikesch will just stop using his claws sooner or later and you just give it some time. Your hand does not look so bloody yet. ;) Hugs and kisses to all your boys !

I'll give "NO!" a try. But I'm afraid he'll learn that as "play is bad!"

When Moritz used his claws while he was on his back and played with my hand (and I can tell you it is not funny to get to know Moritz's claws, they are so sharp he could just use them to remove my liver, if he only wants to ;) ) I have blown a little into his face and he stopped right away . When we do that the cats believe we are hissing just like a cat. This trick worked with every cat I had/have. You can say NO ( only no never Mikesch no) too, louder as you talk usually but that is something you know I guess. No is the word every cat shoud know. But well, no idea how Mikesch would react when you "hiss" because he is not 100 % tame.

The only problem now is when he rolls onto his back to play with my hand, he doesn't retract his claws. Any tips on how to teach him?

Lovely tuxie boy...I don't see any blood, so this is a very good status quo for a feral (formerly!) who was so fearful! Can you imagine how he must have felt?! Great caring job!