Then the real test, how to frame it and attach to a post/column to display at the top of the driveway. The idea to use wood for a frame was tossed when I realized the maintenance involved (weatherproofing, etc.) plus it would be difficult to work with the thickness of the board and uneven pebble edges so a trip to Lowes provided the almost perfect option. The J-channel used for trimming vinyl siding would be weatherproof and flexible enough to fit over the pebble edge. PLUS it was cheap (about $6) and I could paint it!
Mitering the corners wasn't easy without a miter box and even though it's not perfect it worked. THEN to figure out how to make something to attach it to! This project went unfinished for about six months but by November the structure was constructed and the pebble address plaque was finally finished.
In the end I decided not to "attach" the plaque and just position it against the structure....just in case I have any repairs to make with pebbles that might come loose, etc.