For the most part Big Bro does watch over the seaways and knows when a boat makes an approach into US waters.
This is a pretty easy trick here on the west coast where it is wide open sea. No where to run to baby, no where to hide (as the song goes).
But even this breaks down at times. Once in the early 90's Wifey and I sailed into Mission Bay to spend a weekend and were aproached by a harbor patrol vessel in the entrance channel asking us to prepare to be boarded. I had recently had the hull awlgripped black with gold trim and replied to them to let me get my fenders out. This was on a winters day with only the hard core sailors out (musta been 60 degrees out we So-cal guys are kinda spoiled), very little boat traffic.
As he approached closer he sings out "how long have you been out?".
"About 3 1/2 hours" I reply
" Where did you come from?" he incredulously shot back.
"San Diego Bay, Silvergate yacht club" I said pointing at my shiny little burgee snapping in the breeze. Old "Athena" was way to clean and sparkly to have been on any extended cruise.
"Oh sorry, we must have missed you." Was the reply. They waived us on by looking a little stupified.
I guess they were expecting someone else.