Look for the sign on South Street (Route 127A) and park somewhere on the shoulder. I did!
As a boy, I'd come to Rockport by train and walk the lane past Sea View Farm, skirt the golf course, bushwhack through the woods to a trail, pass the water tower, get back on the path, then cut through some more woods to reach my back door on Thatcher Road.
Much of this area is now called Delmater Sanctuary. I'm amazed by the paucity of information available on Google regarding who Delmater was and when this became a sanctuary. I only found out this piece of land had a name by Google Maps.
I've posted a screenshot that you'll find informative about where the trailhead begins, the coordinates and how far the cache is from South Street. There is a sign indicating that someone's driveway is a public path to the sanctuary. Follow the path past some outbuildings, through a stone wall, up between some boulders to a pine grove. The cache is roughly 25' off the path to the right of your direction of travel. The cache is in plain view from the proper angle. There is no need to move anything. Read the hint if necessary.
This was placed as far as time would permit me to explore. There were no muggles out or back on my two visits.
Congratulations to Geo-Knot for the FTF!