if you were looking for some form of self-defense, a spear gun might be a greater threat at close range.
The pepper spray might work too - although (as with other forms of resistance) it could very well enrage
the invader so that he (?) is more prone to violence and destruction.

I've read that some cruisers in a post-hurricane situation fired flares at looters and the flares bounced
off of the looters t-shirts leaving them uninjured [!!!] - then you'd have to worry about the boat burning and
possibly exploding

Now maybe if a bunch of pirate vessels were chasing you and you could jettison huge gas barrels which
would be close to the ppirate boats, you could pull a James Bond ploy a la "From Russia With Love". Nah,
that wouldn't work either (for many reasons, including the fact that I have a diesel engine)- even though it was one of my fav 007
scenes. (Maybe you could substitute propane tanks. Nah, that wouldn't work either.)

Do any of you carry big tacks which you sprinkle on the deck, a la Slocum? With my luck, I'd need to go
topsides for some reason or another and end up stepping on the tacks myself. I think the cat, at least,
would be smart enough to avoid stepping on the tacks.

A well-known cruiser used to advocate carrying sticks of dynamite (in the event of a grounding to
blow a path back to sea) but I can't see that working against a boat invasion. Plus, there's the
question of how you're going to obtain the dynamite. It's not exactly sold by the stick @ WM.
And if a customs inspector found that you were hiding explosives you might find yourself
wishing that you had been attacked by pirates instead.

Actually, what I find most attractive about a 25mm flare gun has nothing to do with self-defense.
It seems like it would be the least dangerous means of firing a flare to the person launching the flare.
(As an alternative, you can use pack welding gloves with your SOLAS flares - which I started doing).
As someone who needs reading glasses reading the instructions on conventional flares - at what
would obviously be a time of crisis - could pose a problem (although, I pack a spare pair of
reading glasses with the flares!). I already have the 12 guage gun (came with the boat) but
it looks kind of flimsy compared to the 25mm gun plus the 25mm flares themselves - although
more expensive - go to a significantly greater height and are much brighter (I think the burn
time is about the same). Maybe I'm just looking for another reason gto buy a new toy....

Jerry