I'm not familiar with it either, but if nothing else, you can pass a counter that shows the number of iterations you've gone through and stop when it gets too high.

What do you plan on doing when you run out of stack space? You can't just replace your code with a cooperate bot or a defect bot after a certain level, since they'll defect if they think you'll do the same thing either way, and you'll defect if you think they'll defect etc.

What you need is something along the lines of cooperating if their code is equivalent to yours, and defecting if it's different. You have to do this in under ten seconds, and you have to get it to cooperate even if they have a slightly different idea of what's equivalent.