I like using Garen top lane and good Nasus is a pain because they all try to freeze lane on their turret where it's hard to harass them.
One game I instead froze lane in front of my turret and punished attempts at Q stacks. He still got them sometimes and also ran off to jungle but our jungler ganked top 3x and Nasus died all 3 (2 kills for jungler, one for me). 3rd kill we took turret and I was level 10 over Nasus 7 (almost 8) with a 15 cs lead for me. Nasus went on to farm jungle + top lane whenever it was pushed and my team still complained to me how he was fed and I lost lane. How going 0-3 with a CS deficit and losing turret while failing to take enemy turret is "fed" is beyond me. We had a chance to win but didn't group for dragon and got wiped/countered.
Next game I fought a better Nasus player who wasn't about to let me freeze lane. Because Garen E pushes I wound trying to stop HIM freezing lane and that's when it gets hard. I couldn't do crap, the only thing that saved me was I got ganked and Nasus tried to dive me...he died and that was the only death in the lane for the entire game. Realizing what I had on my hands I bought wards to avoid another gank and just hard-shoved/pressured turret until I put it down. We were even in CS ffs, so I would argue in this one I was mostly outplayed other than his mistake diving me, yet we won this one because the other lanes did much better and after shoving him I roamed and managed to factor into fights for objectives sooner.
I have no idea how you can pressure him if he's freezing lane under turret with melee champs, other than to do everything you can to keep the wave from settling there in the first place. He has enough sustain to tank you up and heal and keep the wave in place, and you're gank bait there while he can stack Q. As a result I think you need to be really mindful with harass. If you draw too much minion aggro early on his minions will target yours, and as a result not attack your minions which will shove the wave, making it hard to pressure him. Try to limit this or get his AoE on your minions so you can get wave control and harass him without pushing too much pre-6. Nasus q stacking creeps in front of his own turret is worst case, do whatever you can to prevent it.