Tbh, I'd have just dug up the rocks, filled it with some nice absorbent soil, and plant a row of flowers. If the trench is particularly deep, keep a layer of large rocks at the bottom, soil and flowers on top.

And not just the states surrounding them.

Most guns recovered from crime scenes in NYC, for instance, come from VA, GA, and FL. I-95 is just one of several Iron Pipelines in the US.

And then the US as a whole becomes the same for the rest of North America. 3 out of 4 guns found at crime scenes in Canada came from the US. 2 out of 3 guns found at crime scenes in Mexico came from the US. Almost all the border crossing gun smugglers are Americans as well.