Let's see...We used to use red cones at night at border crossings here in North Dakota....and the border outside of the crossings aren't even posted. There isn't even a fence that I'm aware of. People can use snowmobiles or even WALK across in certain area in North Dakota.
THe border patrol has got some work to do.
For a REAL scary map...look at the map of the Lake of the Woods in Minnesota. It will be iced over pretty soon...which means about the middle of January, you can DRIVE across the ice from Canada to the US. That's right...drive across the ice, without any border patrol...at night and right into the USA.
Oh, boy...we've got problems..and they had better get on them quick!
Here in Maine you can drive across from Canada. It's very rural but it can be done. The land is privately owned by logging companies. There are logging roads all over the place and at some point you can't tell when you are in Canada or the US.