In Canada my boat is a private residence, and it is illegal for anyone to come aboard uninvited, without a search warrant. To get one they have to present some pretty convincing evidence to a judge,and that can be challenged. I would never allow anyone aboard . Offshore, some sharp things sticking out, take care of any uninvited inflatables. I once ripped open a US coastguard inflatable that way. The harbour security guard said they would be scrubbing toilets for a while, for that screw up.
I wouldn't cruise any country which allows a bunch of macho foreigners to enforce their own law in their country.
We've had this discussion before on sail net and elsewhere. Canadian laws are indeed different - and in my opinion better for the citizen's protection when it comes to searches.
However, your claims are quaint, but not quiet true.
You can indeed prevent a boarding, however you can also be fined up to 300k for doing so.
The Advocate - Informing Marine Engineers about legal matters
As the article says, it's better to let them on, then make them spell out what they are looking for, and stick to looking just for that.
In both the U.S. and Canada denying a search can be grounds enough for a search warrant, especially in vehicles.
I think under Admiralty law anchored vessels are not homes, they are vehicles in transit (which is why you have the right to anchor). It's only a residence if it can't move (e.g. a RV parked is a RV).
Of course if you stray over the invisible boarder you could also get a couple of 50 cal rounds through your 1/4 steel hull just to make you a little more compliant.