Ryan, that depends on the size of the knife you want to carry and the kind of access you need, like how fast you might want to get it out in a tactical situation, or just for utility.
For example, I have a hunting knife that comes in a leather sheath with a flap over the top of the handle, which is pretty secure. But if I wanted more security, I might get an IWB rig -- "inside the waistband" -- and wear it SOB -- "at the small of the back". With the handle tucked up under a vest, it wouldn't even be visible till I pulled it out. Not the swiftest access, but secure.
Typical of many large fixed blades is a strap that snaps around the handle, and another strap that snaps diagonally across the guard onto the sheath itself. Depending on the strength of the snaps, you may have a hard time releasing them yourself !!
By the way, don't worry about asking one of the standard questions around here. The worst that can happen is someone will tell you to do a search

and the next worst is someone will do the search for you and give you fifty or more old threads to read through ... After all that you will find that some sheathmaker has just come up with something new none of us ever saw before that fits your needs perfectly.
I hope some of our many law enforcement guys see this thread. They've been through it already.