Where do you carry your pen?

I've always kept my pen in my FN, in a cargo pocket, jacket pocket, or in my messenger bag.

But I really prefer carrying my notebook in my back pocket. However, I can't keep my pen there due to the danger of breaking the pen or damaging upholstery.

So, friends, how do you deal with this? If you carry your notebook in your back pocket, where/how do you carry your pen??