As to barracudas, if you're not wearing anything anything shiny and don't panic, they will leave you alone. At least the ones I've been around have left me alone. No trouble from the sharks, turtles, lobsters, lion fish, and other "dangerous" sea creatures I've been around.
But, I did have a pesky icthus obnoxiata, aka shark wah-nah-bee, give me a rough 15 minutes. He, all nasty creatures are "he", kept circling, and circling, looking for an opportunity to attach himself to my poor, tiny body. I whipped out my dive knife and kept jabbing at him. A time or two I grabbed him around the caudal pedestal and attempted to sling him away. Do you have any idea how hard it is to sling a fish underwater? My dive buddy was worthless. He was having a little trouble himself because he was laughing so hard. Choked on the air in his regulator he did. Served him right if he had drowned. Anyway, after a tense hand-to-fin combat, the icthus obnoxiata took himself off and looked for whale shark or some other creature to attach to.
That is the worst trouble I've had in the deep blue. I usually swim off the northern coast of New Guinea, Pantain Harlin, outside of Depapre.