Safe Pitbull Mix My Yellow Lab/pitbull Mix Nails Always Seem To Be To Short?

My yellow lab/pitbull mix nails always seem to be to short? - safe pitbull mix

Daisy dog for a walk on the sidewalk often. What is still not stay on the concrete sidewalk, but despite their claws can grow to a length of safety, they lead to a "fast" fast. Usually within a few days. What gives?