Gonzo also wears his nails down running. However, they can get chipped/uneven from wear, so I clip them usually once a week - after he gets a bath when they're soft. I learned a trick from grooming, for black nails. If you shine a flashlight through the bottom, you can usually see the pink of the quick. Gonzo has half black nails, half white, so I just guage how short the black nails should be by comparison =)
I'm training Fozzie to enjoy clipping atm. He has clear nails, thank gawwwwd. Each time I clip a nail and he sits still, he gets a treat, praise, and a break. Then, in a few minutes, I move on to the next nail. It is time consuming... but hopefully this will make his nail trimmings as an adult much easier.