I don't think you 'defend against' barracudas.

The usual plan is to avoid them and/or to avoid being attacked. At least to avoid providing the signals that cause barracudas to reflexively attack. Mainly avoiding any gear that might flash like or otherwise resemble the small fish barracudas eat.

I don't think an active defense is in the cards. Barracudas are perfectly capable of sneaking up on a person and they are frighteningly fast when they attack. I have had them come within arms length before I caught a glimpse out of the corner of my eye. A four foot long barracuda is Very impressive up close with those teeth hanging out. After I got over awe and admiration I made some noise and it was out of sight, perhaps 40' away, in a flash. I wouldn't have a chance of stopping a fish that can move so fast.

Talking to divers in south Florida, by my estimation, most are more afraid of a barracuda attack than a shark attack.

That harpoon tip, if it is the one I'm thinking of, because it is shiney and vaguely baitfish shaped and sized might trigger an attack. I don't think it is a huge risk and presumably it would be at the end of a pole of some sort but baracuddas are prone to attack anything that even vaguely resembles small fish. I would Not hang it off my body.

I can see a roll for a harpoon of sorts to snag fish in the shallows. Assuming my area had fish suitable for eating a harpoon could be a useful addition.