Oh wow, I had this EXACT thing happen last spring! I found a weird blue piece while digging near my fence. I took a bunch of photos and posted them on a local history group page. Someone there knew it was from a 1970s planter common in our area. Maybe try that, local folks often have the best clues!

Lol, since when do we need permission slips for our own yards? Your neighbor needs to chill, it's not like you built a zombie moat. My rule is simple: if it's on my property, I don't owe anyone a heads up. Unless you're planning to host a rave every night, keep your projects to yourself. People get too nosy about stuff that doesn't affect them. Just smile and nod if they complain again.

Couldn't it work for quick indoor fixes?