Idk how long it will take to cover holes, but if they were filled in enough with the original dirt that one coating of leaves should have covered it so it wouldn't be seen. Imagine how your back yard looks every year with the leaves falling and how much gets covered. I did go back yesterday where I found the buckle. For some reason, the two holes right there the plugs were flipped up again. I know I filled them, and the other holes were still ok. Maybe some animal was looking for grubs (which I saw quite a few there and one massive one yesterday).
Not all sites were hit, but the majority of them were. Think too if they are public land sites, they are most likely hit. Think of someone would be doing research to areas close to him and hit as many as they can in the same general area. That's the answer why certain towns or areas of towns are more hit than others. You find a nice site, you look for more around it, and stick to the areas that produce best. Dan and Bri went to the same spot two weeks in a row. I thought I had a good spot to check last week because there was no pass through of the street. The current road just turns left. The rest of the road is blocked, but it ends at an old bridge which only has the foundation stones remaining. I was thinking that the only way someone knew was to either research it like I did or have been told about it. Sure, it was in a wooded park so public land. There were two horrible holes behind the foundation stones of each cellar. Holes were 2 feet wide and not filled in. I only found 2 of the three sites, while one that I did find looked like it would be an unknown 4th site based upon it wasn't in the location on the map as one should be. I think because there is fishing in the area, that's how someone was told about it and they were hit. I'd go along with what Dan said to consider sometimes a few buttons a win.