Having said that, I also realize the problems associated with that position. Having guns on board in Mexico cost me big time. I was forced to huck a beautiful Ruger SS 357 over the side by my wife after she had a discussion with some other cruisers over the merits of same. I have come to the conclusion that it's more of a problem then it's worth.
Times have changed. Back in the 80's fewer bad guys had guns. Shoot, there were fewer bad guys. No pun intended. Well, maybe pun slightly intended. In the 80's I carried a the 357, a SS Ruger mini 14 which had a collapsible stock and a 30 round banana clip, a fish bat club and a machete. Almost the entire Central America strip was in revolution and you felt like you needed it. I don't know of anyone who I sailed with back then that didn't have some type of gun.
I still feel that you need something to dissuade someone from doing a boat invasion type of entry but traditional guns might not be the smartest way to go now days. Also, you still need to follow the laws of the countries that you are traveling in. Or at least, seem to follow them. I am leaning towards the flare gun. The good old trusted flare gun...almost. In the near future, prior to my next cruise, I will be shooting off several of my expired flares into a tank of water. I will recover the plastic wads and caps. I will take the flare cases to a re-loader and have him reload them with a short load of buck shot with enough powder to get the job done. I will take the aluminum 12 gauge adaptor for my 25 mm aluminum alloy flare gun (with it's locking barrel) to a machine shop and have an exact match turned out in 304 stainless steel.
I'll have flares that will pass inspection by foreign inspectors due to the markings on each case and the adaptor will fit nicely in the slot provided in the flare gun box. I should have at least one shot to get someones attention and then follow up with my one foot long fish bat.
That's going to be my approach and I think, IMHO, that it takes care of the two basic problems. One of legality and one of too much power. I won't blow out a bulk head or shoot a hole in the hull and the flares should pass muster when inspected by the authorities. I hope. Not entirely legal, shoot, not legal at all but it is what it is. Shoot, there I go again.