Knives and shears are needed safety devices. Aqua-Andy has it right. When you dive wrecks, carry multiple knives. You WILL drop your knife when you get caught in mono. It's very hard to see, or invisible. Your heart will beat harder when it happens. Two cutting tools , I believe at a minimum.
When I dive in our local quarry, I just have my small TI knife. The sheath is tie wrapped to my HP hose. There is no fishing allowed there, so chances of mono there are slim. But, when you dive offshore, I have one on each leg, and the one on my hose. When I spearfish, I also carry a wristmount Riffe knife, to dispatch my catch. So, I carry up to four, based on what I am doing.
I know the mono is on the reefs, so I still think it's needed. But when you wreck dive, multiple knives are a must. Don't forget, it's a Wreck Site. That means fishermen who cut or break their lines, and divers who clean up their mess. To all who have cleaned up mono underwater, thanks. Lives have been saved since you do this.
Buy your knives and shears. They are as much as a part of diving as your other gear. Be safe.
