I know where I think it is. I’ve found some of my own relatives living near it in the late 19thC and also wondered exactly where it was since the name wasn’t in use in my time in Newent.

In Census it appears after Church Street but before Upper Church Street and Gloucester Terrace (or Road). This series of streets form the main road leading out of Newent towards Gloucester. If you go along Church Street towards Gloucester you will eventually come to the Black Dog Inn on the right. A little way past this the road turns sharp right. On the left hand side of the corner old maps mark an alleyway leading off with a few houses in it. I’m fairly sure this must be Rocks Alley.

The whole area was redeveloped many years ago and I think even the alley may have been obliterated as well. It might be the modern cul-de-sac of Church Way.

This is the only picture of the general area I can find,

http://speedy1.smugmug.com/History/Newent-Gloucestershire-early/i-DFCxDFF#!/History/New...

It's picture 58 if the link doesn't work properly. Rocks Alley must branch off in the very far left hand corner.