I'll just throw this one out there because it doesn't get much mention on the forums, yet gets high praise from some very knowledgeable folks.....the Gryphon Teruzola M-10 boot-utility. It comes with perhaps one of the better production sheaths. You are asking about the Gerber Guardian, so I though I would suggest something in the same "family", but in my relatively worthless opinion much more utilitarian than the Guardian, and I think, more ergonomic.
Also, I very much admire the Spyderco Kumo, and although there have been some complaints about the sheath, the one I examined seemed to fit the knife and work fine. The handle on the Kumo is very "grippy", the knife over-all light and "fast". It is made from thin stock however, so if you were looking for a fixed blade to "abuse", this would probably not be the best choice.
- regards