I have freedived many a time among countless numbers of bull sharks off the Emerald coast. I used to head out in the morning at about 6AM on the weekends and hit all the bayous with a pair of binocs in search of dolphins. Dolphins were a sure sign that it was safe to dive, as the bull sharks would be moving fast with their 6 towards the dolphins. Alone, smaller sharks like bulls aren't particularly dangerous, but they tend to travel in packs of anywhere from 10 to 50 sharks, and at that number they get aggressive and curious. I've encountered various other species of potentially dangerous sharks and other saltwater marine life, but if you're comfortable in water it really isn't any different than backpacking in wolf/bear/lion territory. I carry a .357 magnum when backpacking, for piece of mind. While freediving, my knife and a speargun were the best I could do. I know more sharks caught my fist than have ever contacted my knife. As I said, at the time I was carrying a 5 inch USMC Kabar with the thick black finish, and it performed well underwater. Was it ideal? Probably not, but I was making E-2 wages at the time, and I probably got more money's worth out of that 30 dollar knife than most people get out of any of theirs.