I'm not a fan of offensive defence against malicious intent (eg guns
, mace, winch
Defensive defence measures in theory include locks, alarms, flak jackets, detectors, etc.
I personally can't see the attraction of sailing if that's what it takes to be safe: I'm very fatalistic about risks (such as weather
failure) which are malice-free, but not at all interested in malicious risk.
The only defensive measure I use, successfully to date, is to avoid parts
of the world where piracy
and boat invasions form any part of the local culture.
Luckily this leaves a huge residual, and frankly other aspects of those cultures have limited appeal to me.