I have a shadowbox fence like this one...
The grass grows in the small gap between the front plank and the back plank. It's impossible to get to and it drives me nuts! The bottom of my fence is all chewed up from me trying to jam the trimmer under there to get it. I hate this fence. If I had any fence/yard experience when I bought this house I would have totally picked a different fence.
BUT, the fucking landscaper who installed this should have known better too. There is a a section of my yard where the fence is about 2 inches off the ground and that is perfect. The string gets right under there. But then there is a long stretch where he put it right up against the ground and there is no space for trimming the grass. I feel like that should be something they are conscious of when installing these.
Anyway, there's my Wednesday fence rant for ya.