Ground rod, one or more?

With ground rods is more the merrier or does that cause problems? I need to do some digging around the main panel at the street to see what's there and if there's a Ufer down at the house I don't know if I can find it. Is it advisable to add a ground rod at the house if there's already one at the street? Also, it's very dry here half the year which I've heard reduces the effectiveness of the ground.

It can take multiple ground rods to effect a decent ground plane. Not sure of the requirements.

from what i've read, you may need two ground rods 6' or 8' apart unless the first one measures below 25 ohms. I had my panel upgraded and the electrician installed two rods and bonded them to the equipment ground in the panel and the 3/4" copper water pipe that services the house.

250.56 requires that there be 25 ohms or it must be two rods. If it is dry then two rods is the rule.