Mmm... I'll chime in for Nasus since he's sort of gaining popularity here and there.
Stack armor and try to last hit under tower. Start boots 3 pots and try to keep your distance. If he starts coming at you with silence try to wither and run, preemptively popping your Q to at least return a hard hit for some lifesteal if he makes it to you. If he's any good your life is going to suck really bad. Rush frozen heart components (all armor items) would be my recommendation. Get tabi too if feasible for the team. You might be screwed if you even go for philo. I saw wicked rush FH vs a Garen and do ok. You can also keep dropping lvl 1 SF on him to prevent his passive from kicking while he's standing back waiting on CDs, could run your mana dry though.
While I love Nasus, especially after reading your guide, he is definitely no counter to Garen. I would call what you describe a clinging to your life with all your might to hopefully not feed, but not countering Garen in a sense where you could deny him free farm and complete lane-control, or even kill.
Like I already mentioned: Renekton and Yorick work very well, and Irelia too (with Irelia max W first and autoattack whatever is in sight, not only lasthitting, to sustain like a boss - get wards to not be a victim of a pushed lane and some armor soon, the difference to Nasus is here that you can actually free-farm too and Garen will stop his harass after a while because he loses CS while trying to hurt you without effect)